[Users] Limit simultaneous calls

Hi, Is there a way to limit the number of simultaneous calls ? According the provider, the bandwith will not permit a lot of simultaneous call so in order to prevent very bad feeling I prefer to limit the use. In a second step, I wondering if this type of restriction can be extended according the phone domain. For example, simultaneous call betwwen two sub-sites of the same enterprise is limited to 10 but all others a limited to 5 for example. I know the ACC module but it's not the one fot this even if the information stored could resolve this point. Perhaps another module already exist ? Thanks, Christophe