T-Mobile says most of its 3,000 stores were overrun on Friday by droves of customers eager to obtain unlocked iPhone 5, iPhone 4S and iPhone 4 smartphones. "Today has been gangbusters for T-Mobile," CMO Mike Sievert told AllThingsD. In another interview, Sievert told Cnet that it was one of the biggest weekends ever for the company.

T-Mobile, America's fourth largest mobile carrier, recently announced a paradigm-shifting contract-free plan offering unlimited text, talk and tethering at no additional cost -- all for $50 per month.

Figures haven't been released yet, but it'll be interesting to get some numbers on just how effective T-Mobile's recent make-over has been.

As part of the change-up, T-Mo also announced it would begin offering Apple's iPhone. Interestingly, it also rolled out an iPhone trade-in program which promises customers $120 credit toward a new iPhone with no up-front cost. No doubt this sparked some additional interest and helped fuel those long -- even if brief -- Friday lines. 

Over a million subscribers had already been unofficially using their iPhones on T-Mobile's network. That's even despite a few drawbacks -- namely limited data speeds, coverage and MMS problems. However, the iPhone 5 being sold by T-Mo boasts a number of important differences which address those shortcomings, like adding 42 HSPA+ fallback and HD Voice calling. Meanwhile, existing iPhone 5 owners hoping to migrate from AT&T to T-Mobile can already do so without much fuss, as GigaOm notes. 

Although currently T-Mobile only covers seven markets with 4G LTE coverage, it is working on expanding its high-speed 4G LTE network to many more cities over this summer.

If T-Mobile's contract-free offering is successful, competing industry monoliths may follow. Verizon said it is open to eliminating contract plans and that it will be closely monitoring T-Mo's success.