I know when I first got my 8310 I could not recieve text messages either, I am also on AT&T I called them and found out that I not only had to have the bb plan I also had to add a text plan, kind of made me mad but if you text alot its worth the extra few bucks a month.
Good Luck & Happy 4th
I get the delay thing too with sprint. Its usually only a few minutes to an hour of delay, but its a pain in the ass. ITL vibrate for like 3 minutes straight sometimes at work. Lol