Calling card agi security

Hi,

I have a calling card script made with php and phpagi. I have blocked the fact that you use multiple phones simultaneously in an account by entering the first caller into the database and outgoing calls are made with

$agi->exec("dial","sip/$dst@outbound_trunk,,L($ms::20000:10000)");

My problem is that it seems like it’s a way around. I suspect that it is dialed at the same time and hits just the second and then escapes the barrier. Does anyone have the same problem and possibly someone who has a solution to the problem?

This issue it is an isolated issue caused by programming logic