RingCentral, a Redwood City, Calif., company that allows small businesses to unify and manage their phone, mobile, fax and email communications, said it has raised $12 million more in a second round of financing.

This follows $12 million raised in Sept. of last year.

The round was led by DAG Ventures and included existing investors Sequoia Capital and Khosla Ventures.

RingCentral said it now has 50,000 active customer accounts, up from 40,000 in September. Accounts range from one to many subscribers, typically in small businesses with 20 or fewer employees, the company said.

RingCentral offers the advanced features of traditional office public branch exchange (PBX) systems plus integrated voice/web applications. Unlike traditional PBX or office phone systems, RingCentral is hosted on the web and is delivered in a subscription-based, software-as-a-service model. Examples of features include:

• Setup and customization in minutes on the web
• Toll-free and local business phone and fax numbers
• Multiple extensions with voicemail
• Call forwarding to any phone
• Message alerts on cell phones or PDAs
• Greetings recorded by professional voice talent
• Optional voice-over-Internet-Protocol (VoIP) lines.