Here’s how call back works     

A callback in this sense is a method of making low-cost international calls via a third country, usually the United States, where call charges are considerably lower.In order to use a callback service, a subscriber is allocated a unique number in, for example, the US, which must first be dialed in order to trigger a return call. This is known (in the US) as a Direct Inbound Dialing (DID) number, or in the UK as a Direct Dial-In (DDI) number. Where Caller ID is available, it may be possible to use the same DID number for many different subscribers, as the callback system will be able to recognize each subscriber's
registered number.

Using our callback services allows consumers to route their international calls through
the a local carrier at US international rates rather than the normal toll rates of the
country from which the call originated. This is potentially very beneficial for people
living in countries with artificially inflated phone rates due to monopoly or taxation.
With our service , you can get this low rates just by using our callback service