electronisa.com reports on a potentially interesting development for T-Mobile customers in the U.S.

US rumored getting unlocked iPhone 4 Wednesday

A SIM-unlocked phone can make voice calls on any GSM network (AT&T and T-Mobile in the U.S.). This is currently a two step process for the AT&T iPhone 4. The first step is to jailbreak the it and then to unlock it. Apple and AT&T frown upon jailbreaking.

However, while the prospect of an approved Apple-provided unlocked iPhone 4 is interesting, it is less practical that it may seem at first glance for two reasons.

1. The iPhone 4 has a micro-SIM card that is not use by most other GSM phones. This means, for example, that you can’t pull the sim out of a T-Mobile phone and put it in to the iPhone without shaving it physically down to fit in the slot.

2. AT&T and T-Mobile use different frequencies for 3G wireless data. Using the current AT&T iPhone 4 on T-Mobile’s network would limit it to the much slower EDGE data network.

However, if this rumored unlocked iPhone 4 worked with both AT&T and T-Mobile’s 3G wireless data network, then it is a much more interesting product release.