The first thing you need to do it workout the extension mappings in Manager, under extensions.
On a 403 the 2 Alog ports are 74 and 78.
Basically you need to count through the extensions in order that they are connection to the expansion ports. This can be confusing for the first time, but gets easy once you have done it few times.
If you had a 406 and a 8 Pots in expansion 1 the first 8 Extions ports would reflect correctly if you sort the extensions via Physical ID, NOT logical ID
Once you have determined your port you need to create a new user under USERS and make the extension number the same as the Physical port under extensions.
If the port is for a FAX/MODEM i suggest ticking ex Directory and turning VM off.
Reboot when free patch and your done
Hope this helps