Opensips cgrates or a2billing VOIP asterisk wholesale retail carrier grade

I am looking for an EXPERT with opensips to build me a carrier grade platform with all the bells and whistles .I also need to an online platform where wholesale and retail customers can purchase DiD and have it automatically provisioned so they can use it on their mobile apps to send and receive calls based on prices on out rate deck. Wholesale customers seeking termination services must be able prepay and send us traffic for termination.. EXPERTS ONLY. I am also thinking of using a2billing for billing.