In mid-July, as Palm Inc. was putting the finishing touches on its new $99 Centro smartphone, the gadget’s development team received a stark message: It wasn’t good enough. The warning was delivered by Jon Rubinstein, a former top Apple Inc. executive who this year joined Palm as executive chairman with a directive from Palm Chief Executive Ed Colligan to shake up the struggling smartphone maker.

Palm, which helped originate the smartphone earlier this decade, has been straining to get back on the right track after stumbling against hipper competitors. Although he officially joined Palm in October, he’s been on-site since July and putting in 70-hour weeks, say people familiar with the matter. Alongside Mr. Colligan, he has cleaned up the company’s product plans, overhauled its engineering staff, and made several strategic new hires.