If you’re using an iPhone and want to change to another smartphone then you may find that your messages go adrift. Now Apple have a new tool for you. It’ll stop messages vanishing by deregister your phone number from iMessage.
When you stop using your iOS based device you can find that messages are still fed through the iMessage system if you don’t disable it properly.
The new tool just needs your phone number, then you’ll get as confirmation message via text (which hopefully you will receive), then you just whack that in and you’re done.
Just head here for the solution.