- 4G LTE is the fastest (Not in the UK yet) Has "theoretical" max speeds of up to 100mbps. It's more like 3.9G but known as 4G.
- HSPA+ DC is dual carrier HSPA+ (Coming to the UK later this year) Has "theoretical" max of 42mbps. Some carriers advertise this as 4G but its really 3.75G. (Most phones show it as H+).
- HSPA+ Currently used on all UK networks (Mostly 3 and EverythingEverywhere), Max speed of 21mbps and again known as 3.75G. (Again shown as H+)
- HSDPA & HSUPA (Shown as H on most phones), max speeds of either 7.2mbps or 14.4mbps. Known as 3.5G.
- UMTS (also known as standard 3G) has a max speed of 356kbps. (Most phones show as 3G)
- EDGE is not very widely used but is 2.5G and has a max speed of around 230kbps. (Most phones show as E)
- GPRS is the slowest and is 2G, has a max speed of 60kbps, most phones show it as a G or a globe symbol.
- GSM is no longer used but was the act of dialling a number to get online, could only show very basic text. It's not 1G as it's still digital so you could say GSM is 2G, GPRS is 2.5G and EDGE is 2.75G.
Hope this helps give you a better understanding of mobile data standards!