I am already using a post paid connection

I am already using a post paid connection in which my STD call rates are high. So plz give me a description of best plan on my mail id. where i can get the STD call on a partcular no. of TATA INDICOMi at very cheap rate. I need to make STD call only a single number of Tata indicom. It does not matter for me if the call rates on another number or also on local call goes high but it should be cheap only for that particular STD Number.