Wirelessly posted (David's Black 16GB iPhone 3G: Mozilla/5.0 (iPhone; U; CPU iPhone OS 2_2 like Mac OS X; en-us) AppleWebKit/525.18.1 (KHTML, like Gecko) Version/3.1.1 Mobile/5G77 Safari/525.20)
It is not, do a full restore. The ringer for phone calls loops the ringtone until the call goes to voice mail or you pick it up. A text message does ring once. There are several tones you can chose. It will ring when you receive the text and 5 minutes later if you have not read it by then, as a reminder that you have an unread text message.
David