What is the maximum number of seed slots you can get in Plants vs. Zombies?
Solution 1:
As per the Plants vs zombies wiki:
Extra Seed Slot ten - $80,000 (unavailable on iOS, Mobiles with Samsung bada OS, DS, and Android because the screen is not big enough to fit it)
If we think about the size of the screen, this may also be why it is unavailable on the Windows phone version.
Solution 2:
Assuming it's the same as other Plants vs Zombies games, 9 is the maximum number of seed slots you can have.