IPhone4 rang twice. Where is it set to ring only once?

1, Settings > Notifications > Messages > Repeated Reminders

If you choose to fold "never", it's ok.

2. You can add the m4r ringtone on your computer to itunes, just like adding music. When synchronizing, check the required ringtone in the "ringtone" column. After synchronization, you can click the ringtone in.

Settings > Voice > You can find your sync ringtone by SMS ringtone. This is limited to os above 5.0. Ios4 and earlier versions can't download SMS ringtones, so they can only be replaced manually after jailbreak.