Why are messages sent from an iPhone arrive on non-iPhones broken into smaller messages?

Yes, a 200 character message sent from a phone with iMessage turned on can arrive as 2 messages on a phone not using iMessage. If iMessage is not on both phones, then the message is sent via SMS or MMS.

The same thing can happen on a message sent from an Android phone. I have a friend with a Samsung Galaxy Android phone who frequently sends long text messages to me and they always arrive as multiple (2 or 3) SMS messages. I don't know who his cellular provider is or it may be something to do with his phone or its settings, but for some reason they are sending multiple SMS instead of one MMS message. What is really weird is that they all show up at essentially the same time but sometimes instead of being in 1,2,3 order they display in 1,3,2 order. Why they aren't being automatically converted to MMS or concatenated SMS, I don't know. http://en.wikipedia.org/wiki/Concatenated_SMS

SMS text messages have a 160 character limit. It may vary by carrier whether a longer message comes in as multiple SMS or a single MMS message.