HSPA is a general name for the High-Speed Downlink Packet Access (HSDPA) and High-Speek Uplink Packet Access protocols. They are packet-based mobile telephony protocols used in 3G to increase data capacity and speed up transfer rates. One of the primary differences between HSPA and EV-DO networks is that HSPA allows mobile handsets to transmit voice and data simultaneously.
Jonathan Morgan has written a very interesting post explaining why HSPA is so important. It all comes down to dollars.