How can I program a land Phone with A timer Software

I need to program a land  phone that can communicate with my timer software installed on my computer.The main purpose of the project is to be able to issue a timer ticket for customers that make phone calls.Such that they can only make calls with the time that have paid for.The project is just similar to a Cybercafe timer Software.
My application will generate a random numbers which  will be used as ticket for my customers.These random number can also be used as  access code for the telephone.Which means that when there is no time available on the time the Customer will not get a dialing tone.If there is time available on the ticket the customer will then get a dailing tone and then dial his number.These number will be sent to my software which will now check the number and apply the  charging rate. I can program with Visual Basic 6 and Visual basic.Net. I am also learning Java at the moment.

Any help please