While Asterisk is a good platform to host agents with their specific advanced features (barging, whispering and other), OpenSIPS may be a better choice for call queuing and distribution. So why not combining them to get the best possible solution? An OpenSIPS Call Center manager is able to host large amounts of queues and agents (and their skills), to queue thousand of calls and to distribute a high CPS to agents, using complex algorithms. But the most important aspects is the ability of such a solution to scale as capacity, but also to be Geo-distributed.