If you get a pda thst takes a sim card and uses GPRS you can get a payt sim card from orange for 1, then top it up and register for the "access to Orange world bundle" this give you 4MB for 4, I just use it for MSN but it can be used for pocket internet explorer GPRS is faster than normal cellular data and you pay for what you download (per kb) rather than the amount of time your online The pda I've currently using is a hp jornada 928 wda, old but works well for what I use it for... satnav, messanger, games and mp3s
Going down this route myself (oooh, a pun!) Getting a 512mb sd card for the recently profed HP Ipaq with wireless internet and bluetooth. I shall also be using the already "aquired" Tom tom 5 software. Need a bluetooth GPS dealie though.