Cisco Voice over IP

How much does it cost to implemant Cisco Voice over IP? Let’s start with the following:

1. Cisco phone system for 3 Commercial locations (within 1 state)with the ability to call each other and make a calls outside.

2. Intially for at least 100 users, but with the potential to expand to 400 users.

3. Also the ability to charge a service to those that use their phones to call long distance.