T-Mobile goes even lower: bring in old iPhone, waive $99 fee for iPhone 5

If you think zero dollars sounds better than $99, T-Mobile has an iPhone deal for you. Starting on Friday, if you trade in an iPhone 4(s AAPL) or iPhone 4S, the carrier will waive the down payment for a new iPhone 5.

Friday is also launch day for the T-Mobile iPhone. It is the last of the major U.S. wireless providers to get the iPhone, and as a result is looking for ways to boost its appeal to potential customers beyond its unusual new payment plan structure.

T-Mobile’s new no-contract payment plans, introduced last month, mean customers can walk out of a store with a new iPhone 5 for $99, with $20 monthly payments for the next  two years. It actually works out to be cheaper than buying an unlocked, full-price iPhone directly from Apple by about $70. The plans are also slightly less pricey than what T-Mobile competitors are offering.

While the pricing does work out to be slightly cheaper, the fact that T-Mobile is getting the iPhone so late in the game — AT&T(s t) has had it for almost six years; Verizon(s vz)(s vod) for two, and Sprint(s s) for about 18 months — means many customers have already settled in with a provider. T-Mobile’s novel pricing plans are intended to appeal to people who may not otherwise have considered an iPhone or a smartphone; but this trade-in deal also could interest people who are at the end of a contract on an older iPhone and could be tempted to find a carrier offering the best deal.

The trade-in offer is available to “well-qualified customers” (those who can secure financing for the payment plan) through June 16.

This post was corrected at 9:39 a.m. PT to reflect that “well-qualified”customers don’t have to pass a credit check, just secure device financing.