Security concerns may not be fully addressed at this point. For example, the Los Angeles Times has the article Square's mobile credit card reader easily hacked, says VeriFone (Mar 10).
Apple Mobile Pay (news link)
MasterCard MoneySend (news link)
Open Mobile Payments (beta) now available to all developers. (news link)
Paypal Send Money iPhone app (news link) now allowing in-app (non-credit card payment) on iPhone and Android devices (news link)