The Nexus 4 is coming, and it supports HSPA+ 42mbps (aka DC-HSPA+). T-Mobile has upgraded a whole bunch of its towers across the nation to support HSPA+ 42, covering most of the major markets. We know a whole lot of people will be considering T-Mobile service with the Nexus 4 launch, so we've compiled a current list of all markets in the U.S. that have the higher speed connection available.
There are 163 markets in total, so hit up the source link to our forums and see if your market is listed.
Source: Google Nexus 4 Forums