HT2109 How can merge sms from old iphone into new one

I have recently purchased an Iphone5. Having set it up as a new device, synchronized it with itunes (music , apps and  contacts etc) while I waited for the phone-companies to transfer and activate my subscription, having used the new one for a couple of weeks.... I realized I would like to merge messages from the old Iphone (3GS- ios6) into the new one,

but how?