You have to do the open source phone first, and help convince others, before the banks and snapchats will support you, not the other way around. It's normally a small sacrifice, but the payoff is fundamental to a free future.
The problem with not using those banks is that I don't think there's any banks that aren't hostile like that, and keeping all of your money under a mattress is a worse choice than compromising on this principle.
But yeah, fair enough! I choose to just not chat to those people, but I totally get that it's not that easy for some.