Common among tech bloggers is a healthy speculation surrounding when the exclusive contract with AT&T will end, and the iPhone will safely land on another carrier. So the latest rumour has the iPhone 4 arriving on T-Mobile later in the year. This parallels the earlier rumours of the popular Apple device going to Verizon.

But the T-Mobile rumour has less legs than the Verizon one, for a couple of reasons. Firstly, AWS band, at 1700MHZ and 2100MHZ (UMTS IV), is not a well-used frequency. In fact, the only places it is widely used in the world are in North America: T-Mobile in the US and WIND/Mobilicity in Canada.

The iPhone 4 is one of the only pentaband 3G phones in existence. That means that it supports 850/900/1800/1900/2100MHZ 3G bands, which covers the majority of the world’s GSM carriers. They purposefully left out the 1700MHZ band making 3G on T-Mobile in the US impossible, even on an unlocked device.

Now why would they decide, after making that business decision to leave that spectrum out, to build a phone with those specifications for a very, very small subsection of North American users? Likely, they won’t. It doesn’t make a lot of business sense, and unless they have enormous financial incentive from T-Mobile, Apple will likely turn down the chance. It would make more sense for them to develop a CDMA device for Verizon, since the market is much larger. And even then, it’s pretty unlikely.

The AWS spectrum is also known for its limited ability to penetrate walls. Couple that with the iPhone 4′s antenna issues and you have a recipe for no service except outdoors. I may be exaggerating, but not really.

But this is just my opinion. I don’t know the inner workings of Apple’s boardroom, nor how Steve Jobs’ mind works. He obviously chose AT&T for a reason back in 2007, and for whatever reason has stuck it out with their spotty service and irate customers.