With the new iphone ios 4.3 version rolled out for update, you can now set the number of times the alert tone should repeat once you get a new SMS on your iphone. The new ios firmware has the option of repeating the alert tones for new sms, this feature was requested by many people via apple forums threads.
To configure this feature you apple iphone must be running 4.3 or later, follow the procedure below.
1. On the iphone home screen, tap settings as shown in the image below.
2. Under settings, go to messages settings as shown in the image below.
3. Under messages you will see the section option which says play alert tone repeat frequency as shown in the image below.
4. Tap Play Alert tone section and then you can set it to repeat twice, thrice, 5 or 10 times when a new sms arrived on your iphone after every two minutes.