When you say you've gone with them for landline do you mean you pay your line rental to them or to BT. If teh former you will find it difficult to get another ISP to supply BB to you. If you still pay BT for line rental but have a dialling code box to redirect your calls from BT through Onetel then there are better ISPs for BB.
As for your 14 minute call to Oz, how would 14 PENCE sound? At that price you could natter for over 2 hours for teh same money.
www.telediscount.co.uk
I use these guys to call Manilla on a daily basis and they are very reliable. You occasionally get a sligh echo on the line so I just redial and its normally fine. There is no sign up or prepayment just dial and go the costs are charged to your normal BT bill.