USSD Services as a VAS in Telco

Hello Guys,

Can any one help with the following-
1.) How to develop USSD applications for GSM operators.
2.) Contact of vendrs who already provide USSD services.

I am thinking of launching USSD services with a Telco in Nigeria which has 20M subscribers. There is money to be made.

Please let me know if you can offer any assistance.