Cannot remove phone number from iMessage

Hi All,

I'm switching phones for a music festival since I don't want to take my iPhone with me, and I'm having a blooming nightmare with iMessage.

No matter what I do - my number always shows up on other iPhones as being "iMessage enabled" - so when I'm using my other phone, I don't get messages sent from iPhones.

I've followed Apple's advice and, with my sim in my iPhone, turned iMessage off. Which did nothing. I've also removed my Apple ID from iMessage and then turned it off - again, it still shows up on other phones as being iMessage enabled.

Any ideas? This whole taking over your phone number business is getting a bit tiresome.

Thanks