I brought a Tom Tom Nav in weekend, wifi one.
Was looking at $500 one with built in sim, but they couldn't tell me if it was 2G or 3G, didn't want to risk 2G shutting down and traffic data no longer working on it. Guessing it would be Vodafone not 2degrees but who knows how long they'll keep 2G.
So got the 520 that uses data on phone so don't have to worry about network.
Pretty happy with it so far, as it can get traffic data off home wifi, so for setting route for fastest way to work don't need to use data on phone anyway, but have that option if going somewhere where conditions might change on way.
More expensive then other options but for Christchurch google maps has got the traffic data wrong at times and also so has here we go, here we go does know the speed limit for part of Tuam Street is 30km/hr where as Tom Tom thinks it's 50km/hr even though it's been 30km speed limit for 2 years, so disappointing tom tom hasn't picked up on that.
Just posting my thoughts on it, and pretty happy with it overall.