There's obviously different fixes working for whatever reasons, etc etc.
To get straight to the point I had the same ' waiting on activation' problem preventing text messaging.
I rang the support section for my carrier, they said that the internet side of things(for that ph number) hadn't gone through yet,( it had been 4 days)...and that they'd get on to it. ...for me to give it about 2 hrs and try signing in again (Apple id) and messaging.
I tried and voila it worked.
p.s Note, I started a new sim card several weeks earlier in a different iphone 4s and everything worked instantly.
...and also on a slightly different tack, my wife's iphone 4s doesn't receive the same amount of signal strength as my iphone 4s when we compare them.