While I generally agree with the point here there's something that need to be corrected. Jason wrote: 'The problem is that the enhanced 3G networks of both T-Mobile and AT&T are based on GSM technology, so they are still voice networks that are essentially retrofitted to handle data.'
This statement is a typical journalistic oversimplification. GSM technology was based on TDMA (time division multiple access) - essentially a time multiplexing scheme. Though GSM was mainly about digital voice even this technology could offer data transmission: CS (circuit switched data). Of course speeds were ridiculous by today's standards (9.6 kbps standard and 14.4 with HSCSD).
GPRS was the next step and it was already an IP based technology. EDGE could deliver higher speeds and then came UMTS AKA 3G. The architecture of these networks has nothing to do with time multiplexing anymore resulting features GSM networks could never offer like video calls, voice and data transmission at the same time etc.. 3G was already designed with mobile data in mind.
Yes, I agree while HSPA+ can deliver really great speeds it is really far fetched to call it 4G network, clearly LTE is the one that deserves thet title so yes, it's just plain marketing to call your HSPA+ (essentially 3G data enhanced) network '4G' no matter how great speeds it offers.
But the 'retrofitted voice network' part is far from the truth.