-HSDPA, HSUPA, HSPA, HSPA+: High Speed Download/Upload Packet Access (+ designates the “Evolved” newer spec). This is a major upgrade to existing 3G networks that allows for (but does not currently actually show) speeds up to 21Mbps at the moment. T-Mobile is using this, and the G2 is currently the only phone using the network, though the MyTouch 4G will as well when it hits the streets. The HSPA+ spec does allow for much higher bandwidths, but 21 appears to be the limit for the short- to medium-term.
-LTE: Long-Term Evolution. This is intended to replace 3G networks altogether, and provides a major speed boost and improvements on the way different types of data are transmitted. Verizon’s LTE-based test networks are currently showing 10-15Mbps, though the technology theoretically supports more than ten times that amount of bandwidth. AT&T is planning an LTE network as well, which they’re planning on launching in 2011, but at the moment they’ve activated HSPA+ at a good number of sites around the country.
-WiMax: Originally rolled out as a wireless home broadband service (i.e. Clearwire), but now being improved to allow for access by mobile phones. The current revision allows for up to 40Mbps, and future revisions promise 1Gbps.