Save money making overseas calls using Hoiio, a callback application by local company Teliwave. The app is free but the calls are not. How cheap is Hoiio? The full rates are here, but as an example, a call to a mobile number to Cambodia is 27.2 cents a minute. Using the cheap IDD services by M1 or StarHub, I normally pay about $1 a minute. Major savings. Have not tried it out yet so I can't vouch for voice quality though. Hoiio is only available in Singapore at the moment.
Ong Jun Da of SG Pools and SG 4D fame is the lead mobile developer of Hoiio. Check out an interview with Jun Da here.