IP Office has a very flexible numbering scheme for extensions, hunt groups and feature commands. While the system has default numbering for feature codes and extensions, they can all be redefined. Default extensions and hunt groups have 3 digit numbers starting at 200 but these can be changed from 2 to 9 digits through the IP Office Manager. There is a default set of feature access short codes, but these can be changed to whatever the end user requires, within limits. This is useful for example if IP Office is replacing a system where DND was accessed by dialing *21, it is possible to change the short code to mimic the code of the replaced system.

In certain countries IP Office can support a secondary dial tone when an access digit is dialed, though this limits some functionality like Alternate Route Selection (ARS). IP Office can also be configured to work without line access digits, by analyzing digits as they are dialed and determining if they are for an internal number or should be sent out on a line - this is valuable in SOHO installations where users will not necessarily be used to dialing an access digit for an outside line.