I'm not sure whether it is illegal to use a mobile phone at 3000ft, but certainly it is unwise. (I’ve heard it illegal, but I can’t tell you which part of the ANO it’s actually stated. Just for interest, if anyone does know it is illegal, could they state where it says it, please). I would not except in very unusual circumstances.
In the UK, we have no method of getting a radar map of the current rainfall - I don't think that even ATC can get an up-to-date rainfall map. I think the most up-to-date rainfall is delayed by about 1 hour. It would appear that in the States things are better. This is a site which I found recently:-
http://www.rap.ucar.edu/staff/pneilley/nids_map.html
As far as in-flight rainfall, there are moves in the States towards getting this (it's called FIS-B - there are other protocols called TIS-B and ADS-B which act to provide you with a display of the traffic around you, similar to that displayed to the ATC). The plans in the states are based on UAT (Universal Access Transceiver) working at 978MHz.
For more information look at
http://www.faa.gov/asd/