I have a desktop application of address diary, developed in C# .Net.

I want to make call from software throw land line phone service, 
in my office we have 8 phone lines, so i want to select line before call,
i want to use headphone and mic in place of phone instrument.

how to connect phone lines to pc. i have more then 8 phone lines 

is it possible ? if yes then how and which hardware i need for this.