Best way to do this:
- Phone MTN (808) and then ask to migrate your number to prepaid. Make sure that they understand this and make sure that they DO NOT CANCEL your number
- In my case it took 48 hours, and other people it varied between 24-72 hours. You will receive a welcome message from MTN
- Once on prepaid, go to a CellC shop (don't use the call-centre or online, or port via SMS, this does not work) - ask for a port (remember RICA docs for the new SIM)
- Wait until your MTN signal is gone and your SIM is deactivated (can take another 48-72 hours). CellC is quite good there, and during delays have actually phoned
- Once the MTN signal is off, pop in your CellC SIM and you are good to go
In all instances where there were issues, it was related to MTN not releasing the MSISDN.