project for skype apis expert

a company sends every day about 100 SMSs to free lance workers. An email-to-sms gateway is used. Each SMS invites the recipient to work at site X at time Y. It is important that the recipient confirms his avaiability. Currently the recipient needs to call a special number. A compamy employees answers the call, the worker identifies himself and confirms he will be available for site X at time Y. This solution is expensive for both the company and the worker. Ideally the worker should just ring number ZZZZ from his phone inside N minutes from the time he receives the sms. There is no need for a human to answer the call. The caller ID will be recorded and the ring will serve as a confirm. This solution can be easily accomplished attaching a cell modem to a company PC. However it would be better to use a Skype number or something of the sort. This way we won't need new hardware (the cell modem) and its maintenance. We need a coder who can setup a software module we can query to get all the phones which called number ZZZZ btw time T1 and T2 (and the time of the call). Please state the coding language you will use. Preferred language is Delphi. Please state the database you will use. Preferred database is Firebird