And you'll be making a beeg mistake!

Dell FTW!
I have been meaning to ask. I decided to take a data bundle and voice contract. Now I take it I will only be getting one SIM card.
Here's the question: if the SIM is in the E220 and I am using it on 3G / HSDPA, what will happen when I receive a voice call to my number?
I have been told you cannot do voice on the E220, but you can do SMS.
Will callers receive engaged tones?
Must I get a 2nd SIM or what options am I faced with to ensure people can still get hold of me while using 3G HSDPA on my notebook?
My work is of such a nature I must be 24 7 365 available, hence my question.