I've seen a lot of comments with people asking why they keep getting a 'H' symbol like it's a bad thing, so here's a basic run-down:
EDGE: 236.8 kbit/s
UMTS: 384 kbit/s
HSDPA: 14,400 kbit/s - 14.4 Mb/s (only in certain places in England, blanket 7.2 Mb/s for Three UK)
GSM isn't included because it can't be used for data transfer, this is usually when the signal bar is shown, with nothing else.
GPRS is pretty negligible, I'd know I get stuck with it all the time in my house. It can load web pages but pretty slowly. This is shown on the N1 with a G next to the signal bar.
EDGE is still 2G but is multiple 2G connections combined. Here's a definition from soul2soul from a quick Google search:
"EDGE is part of GPRS network. During idle state, you will be given 1 timeslot only which is GPRS speed. When you start to download, you will be given more timeslots, hence you notice the sudden increase of speed to EDGE. If you are have lots of data users, you might be given only 1 timeslot. THis way, you might not hit the 220kbps speed consistently. Besides, Edge ping is quite horrible around 450-550 ms at first hop.
3G on the other hand, to my experience, consistentlys hit the 384kbps. It is sort like a guarantee pipeline for you. Of course, the latency is much lower at 150ms to 200ms."
This is shown by an E next to the signal bar.
UMTS is faster than EDGE but is still nowhere near HSDPA. As explained above though, 3G is much more stable than EDGE so you will get a more reliable speed. This is shown by a 3G symbol next to the signal bar.
HSPDA Is the good one. This one supports up to 14.4MB/s. This is shown by a H symbol (on certain ROM's) next to the signal bar.
Personally, I love knowing when I get HSPDA over UMTS since there could be a whole 7Mb/s difference on Three UK, for example; 14Mb/s on Vodafone (some places).
Feel free to comment on any faults and I'll correct them. I did this very quickly
Someone care to comment on LTE?