My phone sends duplicate texts

This is late, but for anyone else wanting to know, this occurs when your message reaches the companies smsc [short message service centre] it fails to send to the recipient at first, so it stores itself on the centre [or logs] and will attempt to send multiple times over the course of the next 48-72 hours depending on how they have their engineering setup. This can result in multiple sms, this is most likely not your handset, but in rare cases with certain phones, like blackberry handsets and some older symbian [vulnerable to hackers] can do this. So call your provider and get them to raise a fault through their networks, then if it fails, look into your handset.

All the time or sometimes most of the time it's not on your end it's the phone company