Compatible CRM with minimum customization

we want to build local cloud Contact center we want to use asterisk as the IP-PBX and then integrate CRM over it,
thus each client will have his own CRM portal and his own short number which will be routed to his extentions.

so what is your advise it nerms of the CRM.

On the CRM part I dont have any suggestion, on the Asterisk integration this is pretty easy task using Asterisk AMI