Why has not arrived yet in the iPhone 4G network?

The acquisition of T-Mobile and AT & T yesterday in the U.S. is resulting in many inquiries. For example, it was confirmed that AT & T will begin using the spectrum of T-Mobile throughout the country in order to supply all customers with proper 3G data network. But that's not all, T-Mobile has always boasted of being the U.S. company with the best 4G data network (the fastest internet connection via mobile phone), so AT & T will connect 4G.

Why Apple has not yet offered on mobile "more futuristic" the market a 4G data network? Just because AT & T and most international telephone operators do not yet have their infrastructure ready for the impending arrival. This step by AT & T may mean that in less than a year, finally, we have a connection iPhone 4G.