Just updated a 3GS to 5 through redsn0w
noticed iMessage cannot be activated for some reason
under settings, it stays at "waiting for activation"

found a few possible solutions that worked for others
Reboot phone
Register another email address

anyone else experiencing this problem?

(baseband 04.26.08)

This seem to be an issue for many people regardless of what iphone they got. My iPhone 4 has the same problem. It worked fine after I just upgraded to iOS5 but stopped working the next day. I tried several techniques that worked for some people but none of them worked, like what you mentioned above, plus changing the DNS settings, etc. I haven't tried a clean install yet. I don't have time to set that up yet.