Enterprise FMC — the ability craved by road warriors everywhere to roam seamlessly between Wi-Fi and cellular networks — just got a push. T-Mobile USA Inc. and enterprise wireless LAN vendor Meru Networks will jointly offer just such a service.

The two companies have completed interoperability testing of UMA-equipped T-Mobile devices with Meru enterprise WLANs to ensure seamless handoffs between the networks.

The idea is to address companies that have employees who use their cell phones as their primary work phones. Routing cell calls over the Wi-Fi network means they don’t eat into cellular minutes.

“The number of mobile-phone-only users in enterprises is expected to increase six-fold over the next four years,” said Phillip Redman, a Gartner research vice president. “This means enterprises need to start looking now for ways to increase the efficiency and mitigate the costs of their voice communication infrastructures. One effective means of doing this is to combine in-building wireless voice with external cellular services.”

T-Mobile’s dual-mode lineup includes devices from BlackBerry, Nokia and Samsung.