IPhone :: IMessages Going To OLD Handset

I've owned an iPhone 4 for the last 2 years, but have now upgraded to a different device.

I still have my old iPhone 4 in my possession, running 5.0.1. I have removed the micro-sim card from my iPhone and it is now in my new device (which is NON-apple).

To my horror, I text a friend (an iPhone user) from my new handset, only for my OLD iPhone to receive his reply! Obviously I was shocked, as my iMessages were set up by telephone number and NOT by my Apple-ID. I didn't understand this, as my phone number (SIM card) is no longer in my iPhone, it is in my new device.

Now having Googled this, I can see that this is something that is affecting a massive amount of people world wide. I cannot believe a company like Apple would allow this to happen, especially with the current world concern about privacy and security!!!

Anyhooo, my question is this: I have my old iPhone 4 in my possession. HOW DO I STOP iMessages going to my old handset?!When the device is erased, will the new owner still be able to set up iMessages as if it is a brand new handset?Once iMessages are prevented going to my old iPhone, will I start to receive messages from my friends as a normal SMS on my new phone (currently this is not the case, ALL texts go to my old iPhone which I ceased using a week ago. EVEN WITH iMESSAGES turned OFF, I still do not receive the message on my NEW device with the SIM card inserted in it)

I have read that removing the sim card, and cycling iMessages (Off then back On) before resetting/erasing. I don't want "maybe's" or "possiblys" in this case. My concern here is my privacy and protection of information that is only for me to see!

Info:
iPhone 4, iOS 5.0.1, SIM card removed to new device.