YAHOO 7 MESSENGER...PHONE CALLS ..AUSTRALIA ?

Ive just D/L & installed "y7 messenger"...need to know a few things (1) if i was to text a friend without the service ..would they receive it ?...(2) is the FREE PHONE CALLS ...PC to PC ..available in OZ ??..(3) If you use it have you had any problems with the service ??...(4) if so ...does this service chew up much credit on prepaid broadband & prepaid mobile phone ?? (5) is it available to D/L to any mobile phone ..regardless of make or model ??.. ANY INFO GREATLY APPRECIATED...THANKS...phil.