we currently have a PRI with ATT and a UC560. we are having issues now that we are opening 2 offices in different cities. we will like to use the same phone system Cisco UC560 but I am not sure it will do the job. I was thinking on switching the UC560 to a Asterisk. I have been told that asterisk has more features for remote locations. the phones we have are Cisco IP phones 7945, will the phones be able to work with asterisk.