VoIP is inherently a networking technology, but also requires an understanding of voice terminologies and technologies. You're probably well-positioned to move into this field, because traditional networking types often have more difficulty grasping and dealing with voice/streaming protocols and services than voice types have with networking protocols/services. I'd suggest digging into networking from the ground up by reading on (or preparing for) the following certifications in this order:
1. CompTIA Network+
2. Cisco CCNA (there's a voice specialty here)
3. Cisco CCDP
4. Cisco CCVP
5. Cisco CCNP
OTOH, if you work (or plan to work) in environments where products/platforms from Avaya, Nortel, Lucent, and so forth will predominate, rather than those from Cisco, you might want to replace items 2-5 in the preceding list with items from their certification curricula instead.
HTH, and thanks for posting,