Making long distance calls can be very cheap whether state to state or international.
When you make a long distance call your voice is digitalized and sent through a fiber optic line to a central database. This database holds a record of your long distance information including your PIC code (Primary Interchange Carrier code); your PIC code indicates which long distance carrier you use.
When you change your long distance carrier, your PIC code will change within the database to the code that represents your new long distance carrier.

Once your call reaches the database it switches to your long distance carrier and switches again to the long distance carrier of the person you are calling. Your long distance rate is then calculated. Simple.
 

Which Economy Long Distance Phone Service?

When choosing a long distance service take these points into consideration: 

1) Monthly fees - Some companies charge a small monthly fee but often charge a cheaper rate per minute. In this case the cheapest service for you will depend on your call volume or the amount of time you expect to spend making long distance calls.

2) Contracts – Normally companies will give you a better rate for a commitment. Therefore you must decide weather you are prepared to make the commitment, sign the contract and go for the lower rate, or weather your would prefer the flexibility of canceling on short notice to see what great offer might be around the corner.  

3) Flat rate long distance - Some long distance rates vary depending on the time of day that you call and this is an important factor that you should consider. If most of your long distance calls are made in the evening then the flat rate is not necessarily the most important factor. Instead you should seek the carrier with the lowest evening rates.