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 5.8 Ghz phone. I'd appreciate any input.