T-Mobile finally joins the iPhone 5 carriers gang and will offer the handset starting April 12, but its version is slightly different.

Until now, T-Mobile simply allowed customers to bring over an unlocked iPhone 5 model from another carrier such as AT&T, but did not carry the iPhone itself. Things have changed, however, and on April 12 T-Mobile will get its very own iPhone 5, offering a slightly different model and experience compared to other carriers.

First of all, T-Mobile recently killed off contracts and shifted to a prepaid, contract-free model. Under this new model, any T-Mobile customer with an unlimited plan ($70 per month) will be able to use the iPhone 5's FaceTime calling feature with no data cap, over both HSPA+ and 4G LTE.

Meanwhile, customers who get bumped out of the carrier's 4G LTE network range will land onto T-Mobile's blazing fast HSPA+ 42 network, which boasts a theoretical speed of 42Mbps down. Speeds of 42Mbps are quite fast, which means future T-Mobile customers should have few complaints once T-Mobile starts rolling out actual LTE.

The iPhone 5 on T-Mobile's network will also sport HD Voice support. Simply put, HD Voice support uses the handset's and the network's hardware and software to reduce background noise and allow for better call quality. To achieve this the feature uses a wide-band adaptive multi-rate codec which delivers more frequency for handling the amound of incoming audio.

Smartphones that are currently compatible with HD Voice include the iPhone 5, Samsung Galaxy S3, HTC One S and, surprisingly, the Nokia Astound. If two handsets communicating with each other support HTC Voice, this neat feature kicks in automatically.

On the other hand, the iPhone 5 is also different from all of the other handsets T-Mobile has to offer. The iPhone 5 will not offer Wi-Fi calling at launch, although that is a key T-Mobile feature. With Wi-Fi calling, T-Mobile customers can make calls for free over broadband.

This may be a drawback for some, but T-Mobile's Chief Marketing Officer Mike Sievert said that Wi-Fi calling will not be available at first, which suggests the feature could become available later on. T-Mobile declined to offer more details on the matter.