How to disable convertins long sms to mms

Jul 17, 2011
MIUI is automatically converting long text messages to mms. I don't like it because I have free sms to some people (I'm used to writing very long messages, 1000+ letters) but not mms. They're not free. And also I'm not sure whether multimedia messages are properly delivered to people outside the country. For example my default settings is not to retrieve MMS when on roaming. Can I disable it?

EDIT: I have a typo in thread title, naturally it's converting, not convertins :)