DiVitas this week will release an improved version of its software application for shifting mobile phone calls between cellular and Wi-Fi networks.

The new version is software only, no longer requiring the original DiVitas appliance. The client code, running on the cell phone, sports a full graphical user interface and support for PBX features. The server code uses a Web-based wizard to fully automate installation, and an expanded set of management policies and features to for monitoring and administering a DiVitas deployment.

The company is offering its software via a hosting service through carriers, with Hartford, Conn.-based Sawtel the first to deploy it. The carrier combines cellular and satellite links for enterprise VoIP and other telecom services in the United States and 16 emerging markets overseas. The DiVitas 2.0 software will be the basis of a Sawtel service that will let business users with dual-mode cell phones roam between Wi-Fi and cellular networks, send and manage e-mail and instant messaging sessions, and access PBX features such as call forwarding and extension dialing.

DiVitas is competing with large vendors, such as Siemens and Research in Motion, and small vendors, such as Agito and Tango, in an area that is not well defined. The products are sometimes referred to as fixed-mobile convergence or unified communications. The overall goal is to pull cellular smartphones more fully and securely into the enterprise voice and data infrastructure, integrate with the PBX, and leverage cellular and Wi-Fi networks to stay connected.

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In Version 2.0, the phone-based DiVitas client has been transformed from a character-based user interface, to a graphical, icon-based UI. Functions can be selected and activated with just clicks, for example. For the first time, the client reveals the user’s online presence and status to other DiVitas-enabled handsets: clicking on the user’s name or icon can make a connection via a voice call, IM or a text-only message based on the other user’s current status and preference.

Also for the first time, the DiVitas client can make use of the battery of features provided to desk phones by the corporate PBX, such as call forwarding, conferencing a group of callers, or putting a caller on hold. All of these features can co-exist with the phone’s native applications, according to Vivek Khuller, CEO and founder of DiVitas.