I can't tell you if this applies to the 3000 series but supposedly the 150 is pretty similar and things I've given out have been pretty close.
If your system has the ability to send out caller-id info (something other than CO trunks) then have a look in the Lines/Networking topic, Routing Parameters tab, and if there is a setting called "No, and type, outgoing" try changing that setting to "local area code" first, and you could always try "country code" if you are overseas - but try the other one first.
As usual, make a note of how it was before you change it just in case you need to go back.
Hope this is close enough to work.