MoVoxx has built an SMS based ad network on the traffic of mobile publishers that send out messages and alerts. It inserts contextually and/or geographically relevant ads into those messages and shares the revenue with the publisher. So it's a way for publishers to monetize "inventory" that would otherwise be simply a part of the service they're offering (e.g., stock quotes, sports scores, flight alerts from an airline).
The company has apparently raised a round of capital (amount undisclosed) to support further expansion. According to MocoNews: "has raised an undisclosed amount in a first round of funding. The investment group includes: Greycroft Partners, Khosla Ventures, First Round Capital and BV Capital."
Yet this copy was already on the site: "Founded in 2006, MoVoxx is backed by Greycroft Partners, Khosla Ventures, First Round Capital and BV Capital." So it's either not the first round or MoVoxx is only now just making the raise public.
MoVoxx clients include brands and agencies.