One of the interesting things to watch next year will be how the cellular and Wi-Fi worlds collide, and a start-up called Divitas hopes to be one of the players in the middle of the action.

Founder and CEO Vivek Khuller says enterprises have done a good job mobilizing office workers by doling out laptops but have ignored one core business asset: the enterprise phone. Despite the ubiquity of cell phones, he contends that 90% of the time the desk phone is still the primary contact point for enterprise workers.

His goal is to make the desktop number portable by extending all the phone's features to a user's cell phone, making it possible, for example, to forward incoming calls to cell phones and dial extensions from those cell phones. Wi-Fi can play a role by helping him do that without driving cellular costs through the roof.

The Divitas product - which Khuller calls a mobile convergence appliance - is a Linux-based device that can be used with programmable cell phones (so-called smart phones) that are cell-only or dual-mode cell/Wi-Fi phones. The latter gives the widest range of options, so we'll focus on that.

When a user is in the office, the appliance routes incoming calls to both the user's desk phone and cell phone. Because the appliance is in constant contact with the cell phone, it can determine if the mobile device can be reached via Wi-Fi, meaning no additional costs are incurred.

If the user is on the road, the appliance determines if the cell phone is available via a Wi-Fi hot spot or if the call has to be routed via a standard cell link. The reverse is true for outgoing calls from the mobile device.

Incoming calls that go unanswered are routed by the appliance to the enterprise voice mail system because that's the number Divitas is trying to mobilize, Khuller says.

But what about when your call is riding the Wi-Fi waves in Starbucks and the guy next to you starts to download a massive file? Khuller says the appliance constantly evaluates the quality of the link and, in the event of degradation, seamlessly hands off the call to cellular. Khuller says it is noticeable by minimally invasive.

Regarding ROI, Khuller says many users make half their cell calls from their offices. So for a customer with 3,000 cell minutes per month, if half can be completed at 1.5 cents per minute using Divitas vs. the average of 7.5 cents per minute for cell calls, the ROI is three to four months, including the $300 for the smart phone.