Who Owns My Mobile Telephone Number?

Hey,

I have been on plans for years now, ive jumped carriers a few times but always had the same mobile number.

I am going overseas in a few weeks & my existing contract with Optus expires halfway through my trip.

I gave them a buzz and they still want to charge me $5 per month (after my contract finishes) to "hold my number" or else "someone else might get it".

Ive had this number for at least 10 years & I HATE the fact that I still have to pay a service even through I have no contract.

Thoughts/suggestions?