SPA-2100 and Multiple Oubound Calls

I just signed up with AXVoice for their unlimited USA and Canada plan.
They are sending me a new SPA-2100. I may not use Asterisk initially
but probably will eventually. I would like my family to be able to make
more than one outbound call at a time. My question is this: Do I need
to be concerned about the type of phones that I will be using? I was
thinking of purchasing a cordless multi-handset 5 ..
Telecom, Cabling and VoIP continues...