Asterisk Caller ID change

Hi, We require the following function, we are using A2billing so the call needs to be correctly rated as other calls are. We are using Asterisk 1.8 & 11, the process needs to be light weight and robust as diallers will be generating the traffic. When specific Outbound CLI's are used its intercepted and the caller ID is changed based on the number being dialler. There is a database with a list of CLI's to watch out for, along with a list of usable CLI's for this campaign associated to a client. There should be 2-3 usable CLi's for each area code for each client which are rotated. For example: Client A dials 0208 555 2020 with CLI of 0845 123 4567 Asterisk see's CLI 0845 123 4567 is marked for the campaign. The dialled number has area code of 0208 so it does a lookup to find a 0208 number that is assigned to Client A for this campaign and proceeds to dial out but now with a CLI starting 0208. So the call now goes out as: Client A dials 0208 555 2020 with CLI of 0208 666 1234 If there is no answer the next attempt would be: Client A dials 0208 555 2020 with CLI of 0208 666 4567