i've got the mex-bt4700 and it's great, not sure what the difference is between the 2700 and 4700 is though, only probs i find is the bluetooth to my phone drops whilst driving sometimes, although this has never happened whilst on a call! the call quality is resonable, i've never heard it myself but my mums quite happy t0 have >1hour conversations over it whilst travelling up the A303/M3, which was more than was ever managed with other setups (this could be a down point to it!), there is also a socket for an external mic iirc. also there is a adapter for the stalk controls, which was a plus point for me buying it, but i've not yet got around to buying the adapter!
Only really annoying problem is, i've got the nokia 5800 and a sony walkman bluetooth m3 player, and it can be quite a job (although not impossible) to get them both connected so phone is hands free and walkman is music, but i think this is the phones problem as it connects with both the handsfree and audio protocols and kicks off the walkman, also related is if u use the phone for satnav then you can't get voice commands and audio as the HU must be on bluetooth audio mode for instructions. although this is solved if you stream the audio from the same phone.
hope it helps
