According to the Philadelphia Daily News:

"It came down between the Yankees and the Phillies," Helms said, and then listed why he chose Philadelphia. "I definitely wanted to stay in the National League. I knew all the pitchers. I knew all the hitters. I know where to play them in the field. Everybody I know who has changed leagues, it's an adjustment period. ...

Apparently, he thinks he'll be happier, too, starting at least part of the time at third base - instead of getting consistent playing time at first base for baseball's most marquee team as the replacement for the departed Craig Wilson/Gary Sheffield experiment.

"The role was to play first base," Helms said. "They were going to DH [Jason] Giambi. On the guaranteed side, they were a little higher [in salary]. But that's just me. I'm going to go where I'm happy. I felt like this is where I needed to be."

Via Steve.