In my startup idea..each customer will have its own phone # and account. I was thinking of a service that can be hooked to customers existing phone # such that

In my startup idea..each customer will have its own phone # and account. I was thinking of a service that can be hooked to customers existing phone # such that they continue paying their existing phone # and I can offer facilities on top of that. I am sure my potential customers are using land line and paying fixed money to get unlimited incoming/outgoing calls. But seeing charges of tropo/twilio it seems potential customers have to switch to pay minute by minute rather than fixed. I think i have to do a good research before I start this project. :)