4th carrier in US
Not to quibble, but T-Mobile is 4th largest carrier behind Sprint...and way behind the giant AT&T/Verizon duopoly.
Given my experience, T-Mobile and the new iPhone pricing, will initiate giant churn at AT&T & Verizon...if they don't react & lower their confiscatory pricing plans.
Customers in US are either too lazy to discern the handset subsidy built into the 2-yr monthly phone contracts (and/or too poor to pay the unlocked price), so T-Mobile has had to shout it out, at a NYC keynote event (while the tech press have been happy to never point it out for the last 5 years). The pricing plans are quite cheaper (with less trap-doors for bill shock).
Note that T-Mobile is the only carrier that offers a lower price for an unsubsidized handset. Clearly, AT&T & Verizon have been raping & pillaging with glee.
Given the spectrum monopolies (and SIM-locking) sanctioned by the captured FCC here, all handsets are unusable on the different carriers anyway (Verizon & Sprint: CDMA; AT&T & T-Mobile on disparate-band GSM, so monopoly pricing abounds.
This is changing now with the re-farmed spectrum that was handed over to T-Mobile, after the AT&T buyout was blocked recently. The tweaked iPhone 5 model that will add AWS-band, will now work between LTE on T-Mobile & AT&T (along with T-Mobile's current 42 mb/sec 3G HSPA+ band). AT&T's GSM iPhone exclusivity since 2007, is finally at an end here.
The idea of the T-Mobile bill amount being reduced, after the iPhone subsidy is fully-paid will astonish phone customers, because AT&T & Verizon have gladly never lowered their bills when contracts expire.
My guess is offering unlimited 3G data -- and merely throttling after your HSPA+/LTE data cap is exceeded -- will allow interesting smartphone app usage, given no more bill shock and overage charges.
Fair-value trade-in for iPhones with no-contract pricing (and $80 cheaper than Apple's unlocked handset pricing) will also allow everyone to upgrade to new iPhone 5S/6 (or new Androids, Blackberrys, WinPho) immediately, as well.
No surcharges for tethering, FaceTime over cellular and easier SIM unlocks for international traveling will be welcome also.
Well done, T-Mobile; six years of nightmarish bills of $100/month (+ overages + 90-minutes customer svc calls to AT&T or Verizon) for SIM-locked iPhones, have finally come to an end in the US.