This was driving my wife mad on her iPhone 4. She got a replacement sim from O2 but no luck, same 2 bleeps every time a message or iMessage came through. Sometimes up to 4 bleeps would sound within 1 second (changing the text alert to choo choo had some fun results, but was still annoying!!)
I had used the phone before her and had no issues so I was certain of a sim fault. My iPhone 4S was perfectly fine, normal single bleeps for message or iMessage. I swapped my sim into her phone, the fault is still there. Oh, a phone problem it must be then.
After trawling the forum I couldn't find a solution, may have not found the right thread on apple discussions. Just while they were in pieces I tried my wife's sim in my 4S, same stupid 2 to 4 bleeps when messages come through. So a fault with then sim after all. But what about the phone?!?
After putting them all back together I received a few messages with my perfectly normal sim in my working iPhone 4S. I now had the stupid 2 bleeps, like it had been infected!
I was at a loss so started looking for info on the carrier settings for certain sims and how they can change the behaviour of the phone, found nothing.
Anyway, decided to Reset, but just the network settings so I didn't have to restore or loose anything on my phone.
Settings -> General -> Reset -> Reset Network Settings, password in confirm.
Restarted quick enough. Problem now gone. Got my wife to do the same and she is now down to a single bleep, as was first intended. Sweet!
Don't know what else the resetting of network settings does except for erase the wifi passwords. I've had no change to my plan, coverage or network availability. Hope this helps others, sorry or the lengthy reply.
