As of today, our phone client is open source. New features, bug corrections, builds for new phones, it's all open for your mad Java skills (or whatever you feel like porting to).
So yes, it's in Java. Last time I tried to get a J2ME toolchain built on Mac or Windows it was 3 days of frustration before I gave up. Perhaps their service API is simple and could be done in Py60 or Mobile Processing.
If you haven't heard of Imity before, the concept is that while geolocating you in the world is neat and all, what really matters is who is near you. It doesn't matter so much that you're at a conference center, what matters is that there are dozen people around you, some of you whom have met already, or will meet again. Imity tracks these proximity locations of other users, connects you when certain ones are nearby.
Really, geolocation is a good mix of the two. Sometimes it is just about me, where I am, and what there is to do there. And other times it's about connecting me with people - and perhaps we go off to do some of the fun things in the area.
Imity also did some very cool stuff by prototyping their concept and code in Second Life, the virtual reality world. It was a great demonstration of using Second Life as a rapid prototyping environment (no need to build into real handsets and find other users in the world), and also did a good job at marketing.
Check out the Google code page for the software.