My suggestion is to call your carrier and see what they can do to shut off your old SIM card so they person who bought it doesn't use it.
Obvious but did you try contacting the person you sold it to yet?
Thanks, everyone for your helpful suggestions!Call ATT and tell them to de-activate the SIM.
Go to this Apple site to sever the connection between your Apple ID and the old 4S just to be safe...
The second is more of a precaution, but I do it for every phone I sell now just to be safe, especially with iMessage bugs/facetime glitches.
lol I did email the guy and he said he could possibly meet me this weekend. Soo, thought I'd be proactive and see what I could do on my end in the meantime.Obvious but did you try contacting the person you sold it to yet?
I'd contact AT&T as well though. With iMessage you want to make sure it doesn't get activated with your SIM in hit.