HSPA+, otherwise known as Evolved High-Speed Packet Access, is the standard for a 4G-esque wireless broadband technology.
The standard is an evolution of HSPA and HSDPA and allows for extremely fast data download rates of 84Mbit/s.
For now, on smartphones, the maximum theoretical speed achievable is 22Mbit/s which should grow to at least 44Mbit/s by next year.
Devices use MIMO/Dual Cell to achieve such high speeds and therefore those with the best connection will be those closest to a tower.
Into the future, HSPA+ will double its theoretical peak speed up to 168Mbit/s.
Additionally, devices using HSPA+ have improved battery life and quicker wake time from areas with no service.
In the U.S., T-Mobile and AT&T use the standard although AT&T is moving towards the "true" 4G, LTE.