Which device? There is a user here that was having the same issue. Happened on 3 or 4 of her phones that were replacements I think. Apparently was an issue with the serial number being entered incorrectly by her carrier, I think.
My iPhone 4 did that twice in the first week that I owned it (it was brand new so I don't think it was dust). It did it once again about twelve months later. I never figured out what caused it. I just reseated my SIM each time it did it and it then it was fine.
Makes no difference if you restore now or after a new SIM, if the OP were to do it now at least they wouldn't be waiting a couple of days for a new SIM when it could be fixed by a simple restore. It probably isn't software related but it's just another option.
He may not need to restore, though. It's only happening a few times a week and he can have a new SIM in two days. It's worth a shot, IMO. I just like to start with the simplest troubleshooting steps first and leave restoring to factory settings for a last resort.
This happened to my hubby on the iPhone 4 first one we got on release day. We tried changing sim card, but had to bring it in to an Apple store. It ended up being a hardware problem. They were good a changing it out. Actually had to change his phone out a total of 4 times in 2 mths. and the 5th time was finally a winner. All were hardware problems.