Expect vigorous tongue-wagging on the subject of mobile network convergence over the next few years, particularly as it pertains to voice. Generous doses of terminology such as \u201croaming,\u201d \u201cdual-mode\u201d and \u201cseamless handoff\u201d will become part of everyday vernacular in this newsletter and elsewhere.Industry players old and new are taking various approaches to expanding the mobility footprint over multiple lower-layer network protocol types, including flavors of broadband cellular, Wi-Fi, WiMAX and wired links. Some efforts to blend networks as transparently as possible for ultimate \u201canytime, anywhere\u201d coverage rely on top-down network infrastructure work by the carriers, both wireless and wired. Others attempt to put roaming control into the hands of enterprise IT staff.Take DiVitas Networks, for example. The start-up last week announced enterprise-centric client\/server software that represents an attempt to mobilize the work phone number (or will, when it ships circa July 2006). A Linux-based appliance or server blade sits on the enterprise premises and inspects all packets in real-time. It purports to blend the corporate IP PBX, cellular network, Wi-Fi network, and dual-mode handsets, which will take on the role of \u201cmobile deskset\u201d when the user is on the move.According to the company, the solution is carrier-, PBX-, Wi-Fi system- and mobile handset\u2013agnostic. What that means is that DiVitas has done co-development work with a number of vendors to make the system interoperate with multiple pieces of equipment and networks. Among them: Asterisk and Cisco CallManager IP PBXs; Cisco, Foundry, Meru Networks, Symbol Technologies and Trapeze wireless LANs; and G-Tek, Nokia, Samsung, and UTStarcom handsets.For now, people who want to reach users on a DiVitas system must call the PBX number and, from there, users can wander back and forth among Wi-Fi and cellular networks. Calling the cellular number at this stage in the game won't deliver the caller into the enterprise telephony system.So the question is\u2026drumroll: Which phone number will survive - users\u2019 cell numbers or their direct-inward dial numbers?