Square's free 'Square Cash' service allows users to send money via email:

Currently, transfer values are capped at $250 per week for the basic service, which can be raised to $2,500 with a few additional steps. While still free, the higher dollar amount requires users send Square their name, date of birth and last four digits of their social security number. Alternatively, a Facebook login can be used for verification.

Okay, free advertising.  I get that.  But other than that, how is this not SNL's Change Bank?  How do we make a profit?  Punchline: Volume.

Debit transactions would go up.  I assume the banks pay for that usage.  Do account holders pick up the tab?  Are Visa and Mastercard paying Square?  Do people receiving money get slightly less than what you sent?  Where's the money I should be following here?