depending on where you are you may be able to get a landline number for free, then set up a voip account on your phone and use it in the same way as skype.

check sipgate for example, but there are a few out there, just google it. i got it for uk and italy.and regurarly use them both at home and on the mover with a n95 first and n900 now.

bear in mind that you drain the battery very easily, but being in an office you should not have any problem getting new juice.