The first 3 of your requirements would possibly be better served with just a good International calling package on your mobile.
Lebara charge £39 a month for "unlimited" calls to 39 countries, including Ireland, and Australia, and cheap(ish) calls to Austria (and other places). Their call charges are pretty comparable to most VOIP services.
It's certainly worth considering if you're spending >£100 a month on calls.
Worth considering for sure and a good idea to investigate similar services more thoroughly.
Unfortunately for Austria mobiles (all rates include VAT):
Lebara: 19p/min
Skype: 11.2p/min (in the £38.99/month for 400 minutes package)
Google Voice: 8.4p/min
Out of the three countries I listed, Austria is the only one I call daily, usually for a minimum of 10 minutes, up to about 20 minutes. Ireland I call infrequently, but SMS up to 10 times per day. Australia I usually call once or twice per week, up to about 45 minutes.
Lebara charge £39 a month for "unlimited" calls to 39 countries, including Ireland, and Australia, and cheap(ish) calls to Austria (and other places). Their call charges are pretty comparable to most VOIP services.
It's certainly worth considering if you're spending >£100 a month on calls.