Changing Extension Number range

When I go to add an extension it gives me options starting with extension 700.  However, I am trying to move from another platform and all my users have an extension printed on their business cards.  I'd like to use the same extension numbers in grasshopper so that I don't have to reprint everyones business cards.  Is there a way to change the available extensionn number range?  I need it to start at 220, not at 700.