I have a new phone but now I need to keep some text messages due to car accident. If I transfer my old number to my new phone will I lose the text messages?
Most likely they'll stay on the old handset. It depends on where they are stored.
I'd not expect a copy of the address book to move them. However there may be the ability to back up the phone data to your PC and restore it to the new phone. May need to download a programme.
Folk may be able to give more help if they knew the mobile models.
It will depend upon how you transfer the number. If your new phone is on the same network as the old one (or it's not locked to a network) and they both use the same size SIM, then you can simply put the old SIM into the new phone and your texts should go with it.