Last September Salesforce.com confirmed its reported acquisition of hosted help desk company Assistly. Tonight Salesforce.com is relaunching Assistly as Desk.com, a new service for small businesses that has been completely rebuilt from the ground up by the Assitly team. Existing Assitly customers will be migrated automatically.

Desk.com features seamless integration with Facebook and Twitter, and an HTML5 mobile application that will enable customer service agents to access the help desk from virtually any mobile device. All Twitter @ messages directed to a company or any comments left on a companies Facebook wall are automatically turned into help desk cases in Desk.com. Agents can respond to customers on Twitter or Facebook from within Desk.com.

Desk.com will follow the same pricing that Assistly switched to last summer. It will be free for just one customer service agent, and pricing will start at $49 per month for each additional agent. Other staff that might need to respond to a customer inquiry can use the service for $1 an hour, enabling a company to provide support from across the company without having to buy an account for every single user that might need to touch customer service. That should help its pricing be competitive with competitors with cheaper per-agent pricing.

Salesforce.com also offers Service Cloud, a customer service help desk for large enterprises. Desk.com is targeted at small businesses.

Desk.com.has its own API, according to VP and General Manager Alex Bard. However, one thing I would have liked to see is compatibility with the Networked Help Desk initiative. Networked Help Desk is an initiative backed by several companies, including Atlassian and Zendesk, to create a common API for multiple applications that may be involved in providing customer service. There’s real value in bringing in people from outside the customer service team – such as sales, marketing, engineering or even executives – to the help desk, and Desk.com makes that very possible with its price scheme. But Networked Help Desk provides a common language for integrating the help desk, CRM, bug tracking, monitoring and alerting systems, etc. It’s building a Web oriented architecture to customer service applications that would make it easier for many applications to be integrated in the future.

Still, Desk.com is a solid offering with an intuitive interface to some powerful features. It competes with services such as Get Satisfaction, Uservoice, Zendesk, Freshdesk. It will be interesting to see how this competition plays out since some of Desk.com’s competitors, namely Get Satisfaction and Zendesk, also sell their services through the Salesforce.com AppExchange.