Changing a work permit, single to multiple entry

I (a non EU national)have got a consultancy job in Germany from June 2007.My managed Agency applied for my work permit which arrived only yesterday.However its a type D visa which is only for Germany(not a Schengen visa) & is a single entry visa only.Now problem is because of my job nature,I will have to travel both within Schengen & outside Germany frequently,therefore it has to by a multiple visa & a Hybrid(Schengen) visa.
Can anybody suggest what should be done to change it to multiple entry & Hybrid?
Whether the complete work permit process has to be started all over again since it takes 3 months to process the application & my company wont wait for that much time?
Any suggestions?

Talk to your employer when you get here ,and get them to work with the corrent Amt, to get you an updated permit.