I am regularly plagued with the problem of completely losing signal on the 4S, even during times when there should be bars. If I go into the settings and manually select Rogers as my carrier, instead of having carrier selection set to automatic, it'll reconnect and I have bars. If I then go back to automatic, it continues to work fine until the problem reoccurs sometime later.
This is annoying and frustrating. Reading on the Internet it seems iOS 5.01 caused a similar problem for some people, but I'm not sure that this is the same thing. Any suggestions?