Some hardware advice for GPS system


I have been playing about with the GPS shield for the Arduino Uno, and really happy with it. But now, I need to step it up a bit -- I need to be able to do some real time tracking. For example, I need to try and build a system that will allow someone who is walking around somewhere with a GPS module to be tracked in real time, by someone in a remote location (i.e. sitting in an office somewhere).

Of course I am going to need the GPS module, but then what? To allow for real time tracking, will I need some sort of GSM module/shield attached with the GPS module, to send the location information?

I would be very grateful for any help and advice, to save me heading off and buying things I don't really need.

Thanks in advance.