Need help on my dad iphone 5.

[papergoat]

The iPhone is from Starhub shop,

1st few months with iOS 6, often reboot.
after iOS 7 update, reboot stop. but when i call him, my side will show engage and his side will show miss call. i got to call again then work.

left 3 months before warranty end. got to solve this ASAP.

 

[PetPet]

Have you tried restoring the iPhone to a clean state?

 

[papergoat]

ok, so i got to back up his phone, restore to clean state, then restore back old data?

 

[PetPet]

ok, so i got to back up his phone, restore to clean state, then restore back old data?

Hmm you can try that.
After which

Settings > General > Reset > Reset All Settings.

Take note, it's "Reset All Settings"

This would remove

Alarms
Selected Keyboards
Selected Ringtones
iMessage Setting (Send as SMS)

 

[kerrying]

Hmmm.. Give reset all settings a try. If it doesn't help, try reset all contents and settings - but this will wipe out every bit of your user data, beware.

It is likely you already have been and used to using iTunes, and updated to iOS7 this way (instead of with OTA, which actually can be pretty flaky and risky sometimes). If it still doesn't help, I will recommend you go the extra long route of using iTunes on Win/Mac, download the entire latest iOS7.x firmware, restore and then set up as NEW, not restore old backup. Assuming you can do without your current user data.