Why does this girl not call me instead of text/e-mail?

It confuses me when this girl (and girls from the past) always text u back instead of calling you back. I told her my text are limited to 100/month (which they are) hoping that she will start calling me instead but she would rather text me anyway or e-mail me on Facebook. Is this some sort of stupid hint?! It doesn't make any damn sense why she, or anyone else for that matter, would do that...