My Wife's Phone had/has this same issue (We are on Sprint). The last time it happened we ended up going in to Sprint and it turned out while we were out of town, Sprint updated their towers in the area and pushed an update out to all Samsung phones that were affected. Because we were out of town she did not get the update.
They were able to fix this by entering some codes in the store and we were out the door in 5 minutes. The rep we talked with said it was something specific to Samsung phones.
NOW since the latest update she downloaded, she is not able to connect again. I plan on calling Sprint tonight to see if this is an easy fix again and if it can be done over the phone or if I need to stop in.
I will report back what I find out.