More than 50 million dual-mode handsets enabling users to talk over a cellular network or by using voice-over-Wi-Fi technology will be shipped by 2009, with enterprise employees expected to be the primary target market, according to report from ABI Research released today.

Combined with a Wi-Fi network that is connected to an enterprise’s PBX, such handsets will allow workers to continue using their cell phones when in range of the enterprise Wi-Fi network.

“As Wi-Fi networks proliferate, it only makes sense to give users the ability to switch from the cellular carrier’s network to the enterprise Wi-Fi network,” said Phil Solis, ABI Research’s senior Wi-Fi analyst, in a prepared statement.