If you want to build a next-generation consumer banking app, and then use it to attract retail deposits, you don't actually need to be a bank.

Simple in Portland, Ore., has proven that over the last couple of years. By partnering with Bancorp Bank, the technology startup has been able to forego acquiring its own charter, while still providing deposit insurance to its customers.

But Simple has bigger ambitions — Chief Financial Officer Shamir Karkal has expressed potential interest in mortgage lending, for example. And eventually those plans may require the company to obtain either a bank charter or state-by-state licenses to make loans and run money services businesses, also known as MSBs.

On Monday, Karkal and Chief Executive Officer Josh Reich took to Twitter to hash out, in an extraordinarily public conversation with tech investors, the pros and cons of Simple's various options.

The discussion started when Reich jumped into a conversation that Silicon Valley legend Marc Andreessen (who co-founded Netscape and the venture capital firm Andreessen Horowitz) and other tech investors were having about banking in a post-branch world.

Karkal replied:

He added:

Reich then shot back:

At that point, Reuters finance blogger Felix Salmon took note of the conversation's unusual forum.

Reich got the last word: