I've had decent coverage with 3 out there but you have to sometimes be prepared to disconnect from networks and connect to others manually. I find it will lock on to one and then that will get crap but you'll still be connected to it rather than a much faster network.
It also depends on the phone hardware. Some only have one or two of multiple bands working so although the coverage is good your phone won't connect as it doesn't have that radio band. This is a good site for checking that http://willmyphonework.net/
I've had decent coverage with 3 out there but you have to sometimes be prepared to disconnect from networks and connect to others manually. I find it will lock on to one and then that will get crap but you'll still be connected to it rather than a much faster network.
It also depends on the phone hardware. Some only have one or two of multiple bands working so although the coverage is good your phone won't connect as it doesn't have that radio band. This is a good site for checking that http://willmyphonework.net/