Yes. By default, Pulse SMS will convert any message that doesn't fit in 3 SMS messages, to MMS. So, if the message overflows onto a fourth SMS message, it will be converted to MMS so that the text comes combined in one message instead of being broken apart.
If you never want your messages converted to MMS or you want to change how soon they get converted, this is configurable in Settings > MMS Configuration > Convert to MMS.