Until now, anyone who's switched from an iPhone to an Android phone may have experienced "vanishing" messages. The reason being that iMessages are still activated, and any blue bubbles sent to you won't actually arrive.
But Apple has finally solved the problem with a tool that'll let you disconnect your phone number from iMessage, should you jump ship to a non-Apple device. You don't even need your old iPhone to do it.
Apple has posted the instructions on its website. You'll need to enter your number into a box, and a six-digit code will then be sent to that phone. Put that number into the next box and - hey presto - it'll be deregisted from iMessage.
If you do have your old iPhone, you can put your new SIM back into the old Apple handset, head into Settings, and switch iMessage off manually.