Blocking an incoming call from an overseas mobile number

[Kimi]

Hi, I have a psychotic ex-GF of my housemate who is recently getting to annoy me heaps by calling or SMS me to ask me to ask him to call her.
Therefore, I really want to block her number so that I don't have to accept any of these shitty incoming calls that I have to pay by receiving them anyway(!) nor SMSes, cause she is living in Australia so the incoming calls especially are charging me of receiving international calls!
She even recently made the calls without showing her number which I just ignored, cause I suspected that might have been her and I was right.
Is there a way to block an overseas mobile number or even to report this kind of thing cause it really gets to be annoying? I do have her mobile number, but unfortunately already deleted the SMSes cause the content I reckon wouldn't make strong enough case to call her a stalker, yet.
But I'm hoping to be able to ask my phone operator here or the operator in OZ to do the blocking.
She actually stalked my housemate and his current GF in Thai by bombarding them with calls and SMSes with much higher frequency.
I'm in the middle of expecting important calls, sometimes can be from overseas too, so that's also why it gets annoying.
The amusing thing is she's actually a public official of SG...

[Plavt]

Try a different phone, I have a Sony Ericsson W300i which has the ability to restrict incoming calls including while roaming.

Ps: I think some of the Nokias offer the same facility too.

[bigfilsing]

just explain to your OZ phone operator that you've been doing the booogaloo with a bird you no longer wish to speak with. Their ozzie surely they understand the predicament you're in

[bigfilsing]

Oh and next time put a little thought into who you give your ( ozzie or otherwise) phone number to.

[MikeDirnt]

you need to install software to block unwanted numbers

[Kimi]

you need to install software to block unwanted numbers

Any recommendation of the software?
My mobile is Motorola btw.

[Kimi]

Oh and next time put a little thought into who you give your ( ozzie or otherwise) phone number to.

That's also the funny thing. I didn't give my number to her.
My flatmate met her by chance when she's back here just for a few days, and then they sat together. When he went to the loo, she apparently took his mobile phone from his bag(!) and checked his SMS inbox. She then found my SMS well making a joke that I met a headhunter here who is more bitchy than this woman, the ex. So she then confronted him about it and then confronted me in one of her SMSes.
Granted, it was a bad joke, my bad, but she's not supposed to take his mobile phone like that without his consent! Psycho!

I really don't understand this woman's brain if she had any... She's so into Caucasian blokes which I can understand how she got to fancy my flatmate. But then clinging to a man who doesn't want to have anything to do with her anymore, when she's in the land full of Caucasian blokes, I don't see the point doing this to my flatmate. It just made him hate her more...