...Apple really, really don't want you using two phones with the same Apple ID. Not sure why. Are there really that many people selling on iphones without wiping them first, that this is a security consideration?
TL;DW - you can do it, but expect Apple to lock the account, screw up iMessage and ask both phones if it's ok if the other can do something every time you change functionality. It might just be easier to create a new ID for the new phone.
