[Freeswitch-users] External SIP profile

Maybe this is a bit of an uneducated noob question (or misunderstanding about SIP) but here goes: If I have an external profile set up and registering, does it essentially behave like a soft phone would behave? What I am running into is incoming calls work fine, but outgoing calls always produce a 404. If I use a soft phone using the same registration I can make calls with no problem (in both scenarios the calls are to/from 4 digit extensions on a Mitel PBX).