I am using a provider (Anveo Direct), which authenticates via IP and allow for multiple route profiles to be setup. They use a prefix in from of a number as a way to select a specific LCR and a security mechanism as well. 3CX doesn't have a way to prefix anything sent to a provider aside from using Outbound Rules. However using Outbound Rules is not idea because that will cause the prefix to be listed in the Call Log, and in general, I believe Trunk specific parameter should be configured in the Trunk settings, not anywhere else. Therefore I suggest adding the functionality of manipulating of information sent via SIP Trunk within the Trunk settings. Anveo Direct Trunk setup 1. Configure Outbound Trunk(s) 2. Send calls from authorized IPs to: [PREFIX]PHONENUMBER@SBC.ANVEO.COM where [PREFIX] is your custom configured prefix for the trunk and PHONENUMBER is destination phone number with country code. Prefix Prefix is used to identify a particular trunk for calls received from a particular IP address. When Anveo Direct receives a call Outbound Trunk will be matched by source IP and Prefix. Prefix is optional but it is STRONGLY recommended. Prefix must start with 0 and it must be 6 alphanumeric characters long. For example: 0aBCdE and 012345 are both valid prefixes. When sending calls to Anveo Direct Trunk you need to include prefix in the dialed phone number.