According to an NPD Group study released today, over 35 percent of US smartphones sold in the fourth quarter of 2011 were 4G-enabled, up from six percent last year. Of course, what "4G" means is up for debate; for the purposes of this study, 14.4Mbps-capable HSPA+ phones like the relabeled iPhone 4S counted. Not surprisingly, then, 62.9 percent of "4G" smartphones sold in the quarter were of the HSPA+ variety, followed up by 20 percent from LTE devices, and 17.1 percent from WiMAX phones. The numbers suggest that WiMAX, once championed by Sprint as an alternative to LTE, is on its way out — only 6 percent of all smartphone sales for the quarter used the technology compared to a high of 10 percent the quarter previous.

There may be little that's surprising in any of those statistics, but, interestingly, for the year the HTC Thunderbolt and the HTC Evo were both the best-selling (and first) LTE and WiMAX phones in the States, respectively. The iPhone 4S was the clearly the favorite when it came to HSPA+. Hopefully the what-counts-as-4G debate is close to an end: Verizon's and AT&T's LTE networks continue to expand across the country, and Sprint will launch its LTE network later this year. Of course, then the argument will be over what we're going to call LTE Advanced.