BT has teamed up with a US company, RingCentral, to offer an Internet-based phone system.

According to BT, RingCentral's software has been designed to let small businesses set up their own phone system with a professional feel without needing to make significant investments in hardware. The software works with mobile, landline and VoIP calls.

Businesses can configure a virtual PBX through a web-based interface, and perform tasks such as assigning voice lines, configuring voice mail and interactive menu options.

Customers can either use a real telephone to answer or make calls or their PC through RingCentral's "Desktop Call Controller." That interface lets users see call logs and launch calls with a single click by a contact's name, among other functions.

Voice mail messages can also be delivered to a user's email, and then played through a PC's speakers. Another feature is fax software that can send faxes from Microsoft's Office applications or from a mobile phone. Businesses will get a "0800" or "0844" main phone number, and calls can be routed to up to 50 extensions.

In the UK, businesses using RingCentral have their choice of two prefixes for their main phone numbers, which then can be routed to up to 50 extensions. One option is "0800," which is a free number for callers but paid for by the recipient, or the "0844" prefix, which is paid for by the caller.

Fees charged to use numbers with those prefixes are how BT makes money from its arrangement with RingCentral, said Ake Nylen, BT's general manager for broadband, VOIP and software-as-a-service propositions in the UK. BT also gets a share of the subscription revenue.

BT already offers professional services for "0800" numbers, but RingCentral's software allow small businesses to do their own configurations online, Nylen said.

While RingCentral offers a VoIP service called DigitalLine for outgoing calls in the US, there are no plans to offer that service in the UK, Nylen said.

Pricing starts at £15, excluding VAT, per month. Calls are charged per minute, rounded up or down to the nearest 30-second increments, the companies said. A full table of charges is available on BT's website.