I just spent 27 minutes on the phone with someone in Cambodia. Using Hoiio, I paid $7. If I had used the local telcos, it would have cost me about $27. The line was clear (maybe I got lucky). Thumbs up for this great service and the nicely implemented iPhone app.
Find out more about Hoiio from its website or from an earlier piece I did on the Hoiio iPhone app. The enterprising Ong Jun Da of SG Pools, SG 4D and SG Toto fame is the lead mobile developer at Hoiio. Read about him here.
Update: I forgot to mention that even though callback service such as Hoiio can be cheaper than conventional calls, this is not always the case. Hoiio charges $0.82 a minute to call a New Zealand mobile number. If you use StarHub's 018 service, it will cost you $0.48 a minute (plus 16 cents a minute for the call). The lesson here is to do your research first before deciding which service provider to use. Not always easy because for some strange reason, the IDD operators don't make it easy to find the rates.