With Wi-Fi coverage continuing to expand and vendors rolling out Wi-Fi-enabled handsets, many in the IT community are now looking for the inevitable next step — seamless Wi-Fi to cell handoffs. While being able to roam freely from Wi-Fi to cell networks clearly has benefits, there are also some potential pitfalls.

The first potential hurdle for Wi-Fi to cell handoffs is getting technology in place that allows the handoffs to happen. Fortunately there’s already a standard called IMS (which stands for IP Multimedia Subsystem and not Instant Messaging Service in this case) that includes building blocks such as Session Initiation Protocol (SIP) that will allow calls to roam from a Wi-Fi network to a cell network. Many carriers are already well on their way to implementing IMS architectures, so network technology isn’t a major roadblock.

So what’s standing in the way of Wi-Fi to cell handoffs? For starters, carriers need to make a business case. At the moment if someone makes a call on their cell phone from their office, the call travels over the cellular network and the carrier bills the caller. With a dual-mode handset, though, someone calling from their office could place the call over a Wi-Fi network within the building and pay significantly less than they currently pay, cutting into the carrier’s bottom line. Ultimately, this hurdle should be removed, because if current wireless carriers don’t offer dual-mode services, VoIP providers such as Vonage could begin cutting into the wireless carriers’ customer bases.

Perhaps the biggest remaining problem for Wi-Fi to cell roaming is more practical than technical. If an employee is making an international call to Paris, for example, from the Wi-Fi network in the office and continues the call as she leaves the building and roams onto the cellular network, she could rack up a very large and unexpected calling charge. Carriers and their customers have to figure out how to get around the issue of how callers roam from a low-cost Wi-Fi network to a relatively high-cost cellular network before