Oh cool...thats all right up my alley...stuff I do in my job too

We are going to use the NAVMAN GPS bluetooth units.
We have companies here in
NZ that designed this...Its pretty similar to would you use there. ITs called IKE. I've had a bit of a play, I thought it was a bit big and heavy, but as with all things, as technology increases, the smaller they get.
http://www.surveylab.co.nz/Who_is_ike~qu.html