Now playing: Watch this: Jumping on AT&T's cheaper unlimited plan? Not so fast...

With Verizon, T-Mobile and Sprint serving up standalone unlimited-data plans, AT&T doesn't want to be left behind.

On Thursday, the carrier announced its own unlimited offering, set to become available Friday for all postpaid customers (people who pay their bills at the end of the month). The company previously only offered unlimited data when you subscribed to its DirecTV or U-Verse TV services.

The speed at which AT&T responded -- coming just four days after Verizon unveiled its unlimited plan -- highlights the competitive aspect of the wireless business. The carriers are tripping over themselves to one-up each other to win your business.

The new AT&T Unlimited Plan includes unlimited talk, text and data on four lines for $180 a month (after $220/month for the first two months). The single line cost of $100, however, is more expensive than any of the other options from its rivals.

With this plan, you can also make unlimited calls from the US to Canada and Mexico and send unlimited texts to over 120 countries. In addition, you can talk, text and use data in Canada and Mexico with no roaming charges via the Roam North America feature that can be added for free.

Keep in mind that the new unlimited plan is not exactly unlimited. AT&T says that after 22GB of data usage, it may throttle down the speed during network congestion, a policy all of the carriers have in place.

Also, the company omits the 10GB of mobile hotspot capability that the rest of the carriers are offering.

If you want to find out which carrier offers the best unlimited plan, here's the detailed comparison.