iPhone battery questions!

My 3GS phone's battery seems to be on it's way out. The charge seems to be running out really quickly now. It's about 18 months old.

Part of the problem is that the battery indicator is way off. It say 60% full and then dies, suddenly, and after turning it back on and having it die again a few times, the "flashing red plug me in" screen appears despite the indicator saying I was above 50%.

I've read a few suggestions on forums to say that you need to completely charge, decharge, recharge, decharge etc a few times for the indicator to get back in synch apparently so I will try that.

But has anyone had to replace their iPhone battery? It doesn't seem to me that Apple have made this an easy thing to do. I see there are third party companies who make replacement batteries but opening the iPhone pretty much means Apple will no longer help you with (doesn't it?). If anyone in Melbourne has replace their battery or knows of a business that will do that I'd like to know. I was going to ask at the Apple store when I have some spare time.


Another question, I'm still under contract, but I could get Optus to unlock my iPhone couldn't I? I want to use it while travelling, but ideally with a local SIM in the foreign country rather than pay Optus global roaming charges. This is my first mobile phone under contract so I'm not really sure how all that works.