Text Messaging / Email Interface

I'm looking to design a single interface for composing & sending a message via text and email.

Given email fields/options like subject, bcc, cc are not valid in a text message, I've been leading towards toggling between two composers rather than just enabling/disabling as needed.

I'm curious if anyone has given any thought to this type of interface and if perhaps you have any examples, either prototypes or in the wild?

Here's an example of the current email composer: