Those people not having a bank account and/or not a credit card, isn't they also less likely to use the internet and less likely to have a smart phone with an internet plan ? I would think many of them lack education as well, so how do we sell bitcoin to them ? Seems like a hard sell to me.
To me it seems bitcoin is best used for online business for now.
Why do you assume that underbanked have no smart phone with internet? I'm guessing people find a way of how to get a smart phone before they find a way to get a bank account IMO...
In general people with lack of resources have less access to technology. As I'm not an American I don't know how difficult it is to get a bank account over there.