While the only successfully scaled mobile payments solution for the underbanked that I’m aware of operates in Kenya, there must be ways to overcome barriers to successful deployments here in the US (or in other places around the world).  Here are some hurdles that I perceive being in the way of a solution that can serve millions:

Customer relationship.  Here both banks and mobile operators own and enjoy strong and primary relationships with customers.  This has made the inevitable partnerships between those key “vendors” tricky.  Visa is trying to help the banks, with big announcements such as this one.

Behavior substitution.  An important reason Western Union still owns the international money transfer business (since 1861!) is because changing consumer behavior is very very difficult.  So, even if mobile alternatives exist (and they do), why fix it if it ain’t broke?  Perhaps mobile balance inquiries, and the like, will get people comfortable with mobile, but not in a hurry.  Consider how iSend has substituted existing domestic bill-pay behavior for an international money transfer.  Very clever and very successful.  What if sharing your mobile phone book could give you access to a lower cost loan?

Unique (leap frog) value.  Clearly gimmicks (like “split the bill when you’re out with friends”) won’t create wide spread adoption.  Unless someone can provide a service on the mobile phone that clearly leap-frogs over intermediary steps (as mPesa does in Kenya) or creates some unique value only available on the mobile phone (think phone leapfrogs credit system, or check cashing at home, or lower interchange due to multi-factor authentication possible on the phone), I think the industry will remain vaporware.

Cash IO.  Most mobile payment systems here don’t actually take out the middle man.   To send money via MoneyGram, I have to pay the MoneyGram agent to get cash in and to get cash out.  To send money via my mobile phone, I still need to pay the MoneyGram (substitute your favorite agent) agent to get money in and out.  In Kenya, the traditional agents have been replaced by a huge network of one-man agents: an individual business person who takes a small commission for loading cash in and out.

Big ROI.  Not very original, but still true.  Given $29B in fees and interest payments by the underbanked, it would seem there is a billion dollar opportunity to add convenience and true (leap frog) value.  If not, we’re not going to see anything at scale.