Since email technology has advanced a lot since 2000, most people have stopped using text mail subscriptions altogether. For starters, a text mails subscriber receives his mails in the form of plain text. This is a sort of subscription that you have to request manually.
Everything that you send to a text mail subscriber is converted into plain text. That means you cannot send media files or links as they might also be converted into plain text. Most modern email services allow you to use text and HTML format for your emails.