Yes, OH has been on it for about 9 months now....pay as you go...good coverage and no problems that I know of. I`ve been with them for about 3 months after my last phone gave up the ghost and am equally pleased.
I am also on T-Mobile a la Snowy Owl. No contract and just put in how much money you think you might spend on calls. I don't use mine on a daily basis so just putting �10 (usually at any supermarket)at a time is all I need to do.
However I expect a very busy user will probably get cheaper calls(long term)with a contract type set-up.
I have also been happy with T-Mobile for several years. There are two places where there is no service, one of which is my home. My home is in an unusual place and I expect all networks have bad reception somewhere. Like the previous person, I top it up at the supermarket occasionally.