On the wireless security side, you should definitely consider the Certified Wireless Networking Professional program's Certified Wireless Security Professional (CWSP) credential, which takes the CWNA as a pre-requisite. The only other real alternative is the SANS/GIAC Accessing Wireless Networks (GAWN) credential, which is a great option but more expensive to pursue than the CWSP. Other wireless- or security-related certs (for example, Cisco's CCSP and CCIE Security, or its Wireless LAN Design and Support Specialist certs) do include coverage of wireless security among their topics (as in fact do certs like Security+, CISSP and so forth).
On the VoIP side, Cisco also offers the CCVP and numerous VoIP-related specialist credentials, as well as the CCIE Voice. Many traditional telephony vendors and technology providers -- such as Nortel, Avaya and Lucent -- also cover VoIP in their programs as well, and some vendor-neutral third-party certs -- such as those from the TIA and NACSE -- include wireless security and VoIP in their coverage, though not necessarily together.
That said, I'm also aware of several certification sponsors that are considering wireless VoIP credentials, but nobody's ready to go public about plans, dates or other specifics at this time.
HTH, and thanks for posting!
This was first published in November 2005