Altec Lansing has quietly begun shipping its new inMotion iM310 portable sound system for iPod. Currently listed as “coming soon” on the company’s website, the iM310 features an integrated iPod dock, a compact, folding design, an auxiliary input jack, and the ability to run off AC or battery power, with the latter offering 48 hours of continuous play from three AA batteries. As the most aggressively priced inMotion speaker yet released…