Redwood City-based RingCentral said this morning that it is in a partnership with Concentric, a provider of web site hosting and other services, to offer its products to Concentric customers. Financial terms of the deal were not disclosed. RingCentral provides hosted PBX services, including phone numbers, voicemail, and Fax support, to small businesses. Concentric offers web site hosting, email, Microsoft Exchange, and other related services. RingCentral is venture backed by Sequoia Capital, Khosla Ventures, and DAG Ventures.