Hi guys, sorry if this should go into the carrier sub-forums, but i figured since the common element was an Android handset it might sit comfortably here also.

My GF has a Samsung Galaxy mini, which is fine for what it is - a low end cheap but reasonably capable phone. It's on Vodafone's 3G network.

I've recently inherited a Sony Xperia x10i from a friend who upgraded (downgraded, pending how you feel about the issue) to an iPhone 4s. I snapped it up with the intention of upgrading my GFs phone - at the time not realising it's a Telecom handset.

I thought i'd give it a go anyway just to see if it would work, as it has a better touchscreen interface, better camera, etc etc etc. I factory reset the phone, put my own VFNZ sim into it, and can successfully make calls, and surf the web.

So i guess my question is: "in practise" what are the perils of running it on the wrong network? I know the two carriers use different frequencies for their networks, but it seemed to run fine from the brief limited test i gave it this morning.

Would it boil down to a speed/consistency/coverage issue? 

Thanks in advance.