UBS analyst Maynard Um today cut his rating on Palm (PALM) to Sell from Neutral, with an unchanged $5 price target.

Um says the company is on track for some new Treo products in the August and November quarters, but that Palm faces an increasingly competitive landscape, with the pending arrival of the 3G Apple (AAPL) iPhone and the expected July launch of the 3G Blackberry Bold by Research In Motion (RIMM).

A Palm turnaround still relies on the success or failure of its new Linux product, he says, which won’t be launched before the first half of 2009 “at the earliest.”

PALM today is down 18 cents, or 3%, at $5.76.