Asterisk Black listing

We need a solution in asterisk that help us block incoming calls with the same numbers (robot calls). We are starting a wholesale VoIP business, but we have some clients that if we have 8 or let say 24 ports open, some times they will send 8 or 24 calls depending on the ports available and all ports will be ringing at the same time with the same number let say (212-347-2222). we want to find a solution to the problem, we do not know if the can be done in the dial plan or using a database that allow just the first call to come thru and block all other call with the same number. we think that a possible solution can be to place all current calls in a database for let say 1 or 2 minutes until the call is hanged-up, and if any new call is coming in, then look into the Database to see if the incoming number is in the database, and if it is, then just block the call and sent a "486 Busy Here" Sip response, otherwise asterisk can place the call as usual.