UK fixed operator BT has launched One Phone, a fixed-mobile service that turns up the competitive heat on mobile rivals in the Small-Medium Enterprise (SME) market.

Employees insert a BT One Phone SIM in their mobile phone to receive all incoming calls on that device regardless of whether they were made to landline, extension or mobile number.

Outgoing calls and data traffic are carried over 4G or BT’s WiFi network.

Currently, BT has an MVNO agreement with EE covering 2G, 3G and 4G mobile network technology. In addition, it plans to launch 4G services using its own spectrum.

Interestingly, BT stated that in “in most cases” it is planning to build a dedicated, pico cell-based mobile network on a customer’s premises to deliver its service. The reason for a dedicated mobile network is concern over indoor coverage.

“BT One Phone’s private network will overcome the common issue of poor in-building coverage. This is the key differentiator from BT,” noted CCS Insight analyst Kester Mann in a tweet.

Any phone with a BT One Phone SIM automatically connects to the dedicated network when in range. When an employee leaves the office, they roam onto BT’s MVNO service on the EE network.

EE recently announced its own VoWiFi initiative to address the headache of indoor coverage, both among consumers and SMEs.

BT is also pushing the cloud-based benefits of the new service, which means mobile users can access features such as call forwarding and hunt groups which are typically only available on a fixed phone system.

One Phone looks set to increase competition amongst the likes of Vodafone One Net, as well as offerings from O2 and EE. “BT’s move raises the stakes in an increasingly competitive UK enterprise market as underlined with EE’s & O2’s recent successes,” tweeted CCS Insight analyst Paolo Pescatore.