my texts and emails gone wrong
Since you still have your old iPhone to hand, you're in the best position to prevent any messaging issues, you should eliminate any funkyness with iMessage intercepting. 


You need to head into Settings > Messages, then look for the iMessage toggle at the top of the resulting menu. Turn it off, and then try and send some messages to contacts you know have an iPhone to make sure it's worked properly. If you're presented with a sea of green, then all's good. 


If you've already made the switch and are still suffering


Grab your phone and ring Apple support – check your local Apple website for the number in your part of the world. Get put through to Technical Support, have your Apple ID handy, and ask them to manually remove your phone number from the iMessage servers.