Updated, Dec. 4, 11:30 a.m.: There is a catch, of sorts. Even with the discounts, you'll have to pay what can be a hefty state sales tax. The tax is on the list price of the phone, which can be upwards of $700 for an iPhone 4 32Gb. In California, that means you're paying about $60 in tax on top of the discounted price -- you won't walk out of the store having spent only $25.

RadioShack is trying to stand out from the holiday bargain pack by offering some pretty steep discounts on Apple's iPhone 4.

Starting tomorrow, Dec. 4th, the electronics retailer will be offering $50 off the iPhone 4 — that would make it $150 for the 16 gigabyte model and $250 for the 32 GB.

But even more surprising are RadioShack's trade-in offers: in addition to the $50 dollar discount, anyone bringing in an undamaged older iPhone 3G gets a $75 credit toward a new phone, and users turning in a 3GS can take $125 off.

That means if you trade in your 3GS ($125) and add the $50 discount, you can get a new 16Gb iPhone 4 for $25 instead of $199.

The deal is available in RadioShack stores only — not via their website — and you need to use their Eligibility Check mechanism to see if you qualify (depends on where you are in your current contract with AT&T).

If anyone's interested, you can also buy a new iPhone 3GS for $50, without a trade-in.

This is an extension of RadioShack's Trade & Save program, which goes year-round and allows consumers to trade in a wide variety of phones in exchange for credit on newer devices. Generally for that program, the value of your trade-in is based on the condition of the phone, and you get less the more scratches, dents and scuffs the phone has.

All trade-ins get refurbished and re-sold in the U.S., RadioShack said.

But in this case, RadioShack is giving a little more leeway on the condition of your trade-in. In essence, it has to be working and can't have a broken screen.

— David Sarno

Photo: A RadioShack in Brooklyn, NY. Credit: Mark Lennihan / AP