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August marks several annual events: the end of summer, the start of school and the beginning of flagship phone season. On Thursday, Samsung announced its Galaxy Note 8 flagship. Just a week before, we got our hands on the Essential phone from Android co-creator Andy Rubin. And within the next couple weeks, it will be Apple's turn to announce the new iPhone.

Now is the perfect time to consider your carrier plan. Which plan is the most affordable? How much are extra lines? Should you get a prepaid plan or a postpaid plan? We are here to help with answers to those questions and more.

Which carrier has the cheapest plans?

All the carriers offer unlimited talk and texting, so your decision will likely come down to the cost of data. Unfortunately, there are no apples-to-apples here. AT&T, Sprint, T-Mobile and Verizon's data plans are all slightly different.

The handy chart I made below should help. It compares the total cost over two years on each carrier except T-Mobile -- more on the "uncarrier" later. To make things as easy as possible, I added up the costs of carrier activation fees, monthly line access charges, financing a new $649 phone (the price of a 32GB Google Pixel or iPhone 7) and a monthly data plan over 24 months -- this does not compare taxes, surcharges or other regulatory fees (and my sanity hopes you'll understand).

Total cost for a single line and a new phone over 2 years Carrier One-time activation fee Monthly cost of $649 phone Monthly access charge Monthly data plan Total cost over two years AT&T Next Every Year Plan $25 $27/month $20/month 3GB for $40/month $2,115 ($88/month) Verizon Plan $30 $27/month $20/month 5GB for $35/month* $1,998* ($83/month) Sprint Installment Plan $25 $27/month $25/month 3GB for $25/month* $1,880* ($78/month) Sprint 18 Month Lease $25 $27/month $25/month 3GB/month for $25/month* $1,418* (18 months at $79/month)

* includes $5/month autopay discount

What about T-Mobile and unlimited data plans?

I didn't include T-Mobile in the previous section because the carrier only offers unlimited data plans. In fact, all four major US carriers offer unlimited data plans. Sprint has one unlimited plan while AT&T, T-Mobile and Verizon each have two unlimited data plan options: an entry-level plan that limits video streaming to standard definition and omits LTE hotspot use, and a more expensive option that competes with Sprint's unlimited features.

Josh Miller/CNET

Here's a chart comparing the total cost between carriers of a new phone and a single line on an unlimited data plan.

Single line unlimited data plans and cost of new phone over 2 years Carrier Data throttled after Video steaming One-time activation fee Monthly cost of $649 phone Unlimited data monthly cost Total cost for single line over two years AT&T Plus 22GB/month 1080p HD $25 $27/month $90/month* $2,834 ($118/month) Verizon "beyondunlimited" 22GB/month 720p HD $30 $27/month $85/month* $2,719 ($113/month) T-Mobile One Plus 30GB/month 1080p HD $20 SIM starter kit $26 upfront, $26/month $75/month* $2,470 ($103/month) Verizon "gounlimited" 22GB/month 480p SD $30 $27/month $75/month* $2,470 ($103/month) T-Mobile One 30GB/month 480p SD $20 SIM starter kit $26 upfront, $26/month $70/month* $2,350 ($98/month) AT&T Choice 22GB/month 480p SD $25 $27/month $60/month* $2,114 ($88/month) Sprint 23GB/month 1080p HD $30 $27/month $50/month* through March 2018, then $60/month* $1,999 ($83/month)

* includes $5/month autopay discount

A warning: There's definitely some fine print here.

The plans for AT&T, Sprint and Verizon do not include taxes, surcharges or additional fees.



All of the plans include a $5/month autopay discount.



T-Mobile One and Verizon "gounlimited" limit people to standard-definition video and only 3G hotspot support.



AT&T's Unlimited Choice plan limits people to standard-definition video, data speeds capped at 3Mbps and has no hotspot data allowance.



Verizon and AT&T limit data speed and priority access after 22GB, Sprint after 23GB and T-Mobile after 30GB.



At the time of this writing, Sprint's promotion expires March 31, 2018, and a single line will then cost $60 per month.



T-Mobile One, Sprint and AT&T Plus include 1080p high-definition video streaming with their plans. Verizon's "beyondunlimited" plan gives you high-definition video streaming but only at 720p. AT&T Choice, Verizon "gounlimited" and T-Mobile One limit you to 480p standard definition (think DVD quality).

All the carriers include a mobile hotspot allowance with their unlimited plans. Verizon's "beyondunlimited" gives you the most 4G LTE hotspot data with 15GB per month. Sprint, T-Mobile One Plus and AT&T Plus allow up to 10GB of hotspot data. T-Mobile One and Verizon "gounlimited" includes hotspot data support at 3G speeds and AT&T Choice does not include hotspot data.

Additional line costs for unlimited plans are all over the place. Both AT&T Plus and Choice offer a second line for $55/month and additional lines up to 10 for $20/month (unless it's for a wearable then the cost is $10/month). Sprint gives you a third, fourth and fifth extra line for free until March 31, 2018, after which Sprint's unlimited plan reverts back to regular pricing: $60/month for first line, $40/month for second line and $30/month for lines three through five.

Below is a chart comparing the various prices of adding extra lines to your unlimited plan.

Comparison of carrier additional line costs for unlimited plans Carrier First line cost Second line cost Third line cost Fourth line cost Total monthly cost for four lines Verizon "beyondunlimited" $85/month* $75/month $20/month $20/month $200/month* AT&T Plus $90/month* $55/month $20/month $20/month $180/month* T-Mobile One Plus $75/month* $35/month $46/month $24/month $180/month* T-Mobile One $70/month* $30/month $41/month $19/month $160/month* Verizon "gounlimited" $75/month* $55/month $20/month $10/month $160/month* AT&T Choice $60/month* $55/month $20/month $20/month $155/month* Sprint pre-March 31, 2018 $50/month* $40/month $0/month $0/month $90/month* Sprint post-March 31, 2018 $60/month* $40/month $30/month $30/month $160/month*

*includes $5/month autopay discount, a $10 monthly discount for AT&T

Are prepaid plans a better deal than postpaid?

It depends on the carrier. Up to this point, all the carrier plans mentioned in this article have been postpaid -- you pay monthly after you use the service. Prepaid plans are also monthly, but you pay in advance for the data you think you will use. If you need more, you buy more. Prepaid phone plans also don't have a contract.

Sarah Tew/CNET

What really makes prepaid plans cheaper is the lack of a monthly line access fee. Over two years, this fee can cost you as much as $600 on a postpaid plan. Carriers make up for the this fee by charging more for data. AT&T and T-Mobile prepaid plans will save you some money compared to their postpaid ones, while Verizon's prepaid plan is pretty close in cost to its postpaid plans. And even though Sprint's prepaid and postpaid plans are ridiculously cheap, you can save hundreds by going prepaid.

Downsides

So what are the downsides? The process of constant filling and refilling your data plan can be exhausting. Though, there are options for autopay. AT&T will even give you a $5/month discount when you use autopay for a prepaid GoPhone.

Another downside is the lack of family/multiple line options and pricing. Handset selection can be a negative, too. Sprint has a limited number of phones that work with its prepaid plans -- the newest prepaid flagship phones available are the iPhone 5S and the Samsung Galaxy S3. On the other hand, AT&T, T-Mobile and Verizon offer prepaid access to newer phones like the iPhone 7 and Samsung Galaxy S8.

Both Verizon and T-Mobile offer prepaid plans with unlimited data. Verizon's "prepaidunlimited" plan costs $80/month which is $5 more per month than its "gounlimited" postpaid plan. Verizon's "prepaidunlimited" plan lacks tethering, mobile hotspot support and only offers 480p standard-definition video streaming.

The T-Mobile prepaid plan, aptly named One Prepaid, costs exactly the same as its One Plus plan: $75 per month. T-Mobile One Prepaid doesn't include support for LTE hotspot data and limits video streaming to 480p standard definition. You do get support for hotspot data at 3G speeds and you can buy a high-definition video day pass at $3 a pop.

The chart below compares the cost for prepaid plans on AT&T, Sprint, T-Mobile and Verizon. The cost includes activation fee along with monthly data plan charges for 24 months, but it does not include the cost of your phone.

Prepaid plan comparison (without cost of phone) Carrier One-time activation fee Monthly data plan Total data plan cost for two years T-Mobile $10 SIM starter kit 3GB for $40/month $980 AT&T $25 + $5 SIM card 3GB for $40/month* $990 Sprint $0 3GB for $45/month $1,080 Verizon $0 5GB for $50/month $1,250 T-Mobile One Prepaid $10 SIM starter kit Unlimited for $75/month $1,810 Verizon "prepaidunlimited" $0 Unlimited for $80/month $1,920

* includes $5/month autopay discount

How does Google's Project Fi fit into all this?

Josh Miller/CNET

Project Fi is Google's high-speed phone service that uses a combination of Wi-Fi networks and data from carriers like Sprint and T-Mobile to always keep you connected. The unlimited talk and text plan costs $20/month ($15/month on a family plan), which is similar in cost to the line access fees that AT&T, Sprint and Verizon charge on postpaid plans. The data rate is $10 per 1GB.

These prices apply internationally, too. Google Fi is supported in over 135 countries, so if you're traveling abroad you pay exactly as much as you'd pay at home.

Project Fi has no contracts and works a bit like a prepaid plan where you pay everything up front. If you have leftover data, your account is credited with whatever you didn't use. So you only pay for what you actually use. That's nice.

The downsides with Project Fi are that it only works on the Pixel, Pixel XL, Nexus 6P and Nexus 5X phones and connectivity might be spotty in areas where Sprint and T-Mobile's coverage is thin.

Is it true that I can save money by setting up automatic payments of my bill?

Screenshot by Patrick Holland/CNET

Yes, it is true! All four major US carriers offer a $5 monthly discount for letting them automatically deduct money from your bank to pay your bill. Over the course of two years, this discount can save you $120.

However, there is some fine print here. Verizon only offers the discount for its unlimited plan as well as certain single line data plans. AT&T limits its autopay discount to its unlimited plans and prepaid GoPhone plans. AT&T does increase that discount to $10 a month for an unlimited data plan with multiple lines.

I'm still not sure what plan is best for me, what should I do?

This has been a comparison of pricing for the major carriers, but smaller carriers' pricing can sometimes be equally competitive. The costs of a carrier phone plan is only part of the bigger picture. For many, a network's coverage and data speeds are just as important, if not more so. It's also worth asking around to see what your friends and family's experiences are with a particular carrier, too. This is especially important if you're entering into a family or sharing plan with them. But ultimately, it's your decision. If you think you're paying too much, you probably are and should start shopping around. If you're happy with what you got, consider sticking with that carrier and plan.

If you still haven't considered where to buy your phone or if you should get an unlocked one, we can help with that, too.

Links to each carriers unlimited plans: Sprint, AT&T, T-Mobile and Verizon.

First published Feb. 17, 5 a.m. PT.

Update, Mar. 9 at 9:00 a.m.: Adds a change to T-Mobile's data cap from 28GB to 30GB per month.

Update, Apr. 27 at 11:03 a.m.: Adds Verizon's prepaid unlimited data plan.

Update, Apr. 28 at 12:03 p.m.: Adds T-Mobile's One Plus plan and updates details for T-Mobile's One and One Prepaid plan.

Update, Aug. 25 at 5:00 a.m.: Adds new Verizon unlimited plans and names.