With no other information from you, I would go for the voice cert over wireless.
VoIP is the real growth, and will keep the same sort of technology for the forseeable future.
Wireless systems are changing to mesh and WiMAX systems, and possibly others on the horizon.
So I think the Voice one will be the better one long term.
Looking on the certification tracking system , it looks like you need the full CCNA + the voice or wireless to get these certifications.
Agreed Blank – Get the CCNA R/S (routing and switching) first, as the rest of the Cisco tracks are based on the CCNA. Voice is a great choice, or you can go deeper and hit the CCNP R/S