Expense and time tracking web application Harvest will announced tomorrow that it has added Twitter support. The new service will let users update tracking entries via Twitter from their mobile phones. The web page for the upcoming feature sports a "Powered by Twitter" logo and made us wonder: could this be a glimpse into a future business model for Twitter?

The Harvest-Twitter mashup works via a robot that users send direct messages containing new entries for Harvest. Once users link their Twitter account to their Harvest account, they can direct message commands to a Harvest Twitter client, which right now supports the adding of expenses (i.e., for adding a business lunch from the road) and the stopping of the software's tracking timer (i.e., if you just left the office and forgot to punch out).

It doesn't look like Harvest on Twitter supports starting the…