Cisco Router config for ACME PACKET

 authentication username -snip- password 7 -snip-
 registrar dns:realm.domain expires 3600
 sip-server dns:realm.domain

voice service voip
 no ip address trusted authenticate
 allow-connections sip to sip
 no supplementary-service sip moved-temporarily
 fax protocol pass-through g711alaw
 modem passthrough nse codec g711alaw
  localhost dns:realm.domain
  outbound-proxy dns:sip-server

Note: realm.domain doesn't have to be real(public) domain.
Each phone-dn will have own registration.