5.    SIP is used by enterprises and carriers alike.
Since SIP transcends the carrier-enterprise boundaries, it is likely to attract applications developers able to deliver their core applications technologies in a variety of value packages to address different financing models and markets. For example:

•    The stand-alone enterprise market, addressed by direct sales or resellers;
•    The stand-alone consumer market, addressed by retailers, online or direct marketers;
•    The hosted service model, sold to carriers but billed out to enterprises in monthly charges;
•    The hosted service model, sold to carriers but billed out to consumers in monthly charges; and,
•    The stand-alone enterprise market, addressed by carrier enterprise equipment sales organizations.

This multi-market model gives plenty of space for initial focus, depending on the vendor strength and skills, and presents considerable opportunity for startups and established developers alike.

This commonality across multiple markets also enables innovation in carrier services aimed at enterprises. For example, SIP trunking services allow two SIP-empowered enterprises to communicate using RTP from endpoint to endpoint without the use of a gateway between them. The growth of this category of service can only reduce costs since it reduces load on packet-circuit gateways, and since these services have little or no regulatory and tax burden.

SIP trunking also improves audio quality since bandwidth allocation can be negotiated end-to-end instead of end-to-gateway-over-digital-to-gateway-to-end. Fewer digital hops with more bandwidth enables wide-band audio quality. Of course, SIP-initiated video conferencing is similarly enabled.