Uh oh, Paypal; looks like you’ve got a new challenger in the person-to-person payments space.

American Express has just announced the launch of their new money spendin’ service, Serve. At its foundation, it’s just a fancied up PayPal, allowing users to send one another money via e-mail address (as long as both users have Serve accounts.) Past that point, however, it’s got a few cool twists; you can pull funds from your account into a refillable pre-paid card, or you can create “subaccounts” that let other users (say, your kids) spend monies from your account while you limit and monitor everything that goes down.

With today’s launch, they’re already offering up payment applications for both iPhone and Android.

Given PayPal’s almost exclusive dominance of this market, there is by all means room for competition — but it’s certainly not as if others haven’t tried. Remember Obopay? Yeah — bet you didn’t know that still exists.