SCIENCE!
If they wear space suits, there's prolly no air.
No air = no sound = no phone ringing = good reason not to answer the phone!
Or: 'Sorry, dear, I can't hear you very well, I'm in a vacuum.'
EDIT: Oh yeah, nice pic. Me likey!
(
RarelyEvil,
Sun 2 Aug 2009, 19:17,
archived)