Yes. By default, Pulse SMS will convert any message that doesn't fit in three SMS messages, to MMS. So, if the message overflows on to a 4th 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.
