Thats a mobile phone too i think isn't it. There are plenty of just PDAs and quite a few PDA/mobiles too. I think they are pretty much stuck with the std operating system but you can get different makes with different OSs. Most of the major satnav software is available for most of the major OSs. You will need a GPS aerial of some sort (unless you get a pda/phone with GPS antenna built-in) which can be wired or bluetooth. If its a phone you're after you should be able to get it free (on an appropriate contract) and then get the aerial and the software. If its just a PDA there are many second hand but you will want to have a memory card slot to store maps etc.