Many US iPhone owners are annoyed with AT&T as a service provider, but aren’t willing to accept the limitations of the Verizon iPhone 4. In fact, T-Mobile USA reportedly claims that there are now 1 million unlocked iPhones running on their network.

I haven’t seen any actual evidence backing this up, but judging by the fact that there is reasonably high demand for unlocking solutions (and that Apple has recently released an unlocked iPhone 4), it doesn’t surprise me. The rumor goes that a T-Mobile spokesperson offered up this claim just ahead of the NYC Pepcom event.

When asked for a breakdown, the spokesman admitted that most of those phones were models earlier than the iPhone 4, but that there were still a significant number of people who had trimmed down their T-Mobile SIM cards to the new Micro-SIM standard to use them in their unlocked iPhone 4′s.

Users running unlocked iPhones on T-Mobile’s network are not able to take advantage of T-Mobile’s 3G or “4G” speeds, and the iPhone’s Visual Voicemail feature also won’t work for those users, which seem like pretty significant limitations to me.

If T-Mobile’s quoted numbers turn out to be accurate, it might be worth it for Apple to look into supporting their network’s 3G and 4G protocols. That is, unless AT&T is allowed to buy out T-Mobile USA, in which event all such concerns will evaporate.

Your thoughts? Sound off in the comments!