Paypal mobile uses your paypal account.
It works a few different ways. Not a great way overall, but I have tried it out, so here goes...
As someone who knows about the Paypal Mobile and wants to use it, you have to register your mobile number.
As someone who isn't registered, but got money sent to their number, you get an email and have to sign up for a paypal account, register your phone and I'm pretty sure to receive the money you have to verify your account with a bank account.
To pay someone advertising that they accept Paypal Mobile payments, you have to have or sign up for, a Paypal account, register your phone, fund your account with a credit card or bank account and send the money.
Overall, a complicated solution...