Someone will send you an SMS but you won't get it...it will just drop. Other SMS's will be fine but it's worrying as you don't know which ones will go through or not. This happens 1 in every 100 or so??
Happened to me yesterday. My dad (on o2) sent a text to me (on 3) and my brother (on o2). Bro received it, I didn't get anything. Tried twice with the same results. Very odd.