Cousin B moved back to England from Australia, got an Iphone and is happy with it.

2 years down the line, she's back in Australia (no jobs, bad pay, the usual) still clutching her iphone.

What number should we be dialing to speak with her? Is it the 11 digit one we used while she was here or is it something else?

Thanks

If she has the same UK SIM card, then yes, you dial the old UK number.

However, if your cousin has any sense she would have bought an Austrailian SIM so local calls don't cost a fortune. There are all sorts of other questions though; is her iPhone locked to one carrier? is she still under contract? Has she sold her phone?