The phone informs you when you are about to exceed number of characters for each message (the number ~20 appears in the upper corner of the display). But if you type one message and phone send two or three messages, that may happen if you are using national chars in your messages. While writing new message press "More" > scroll to the bottom of the list > choose "National chars." > and set it to "off"

I don't think you can use text titles for your messages, and do you really need it anyway? (don't need to answer)

Yes, you can unlock it to work on any provider's network. W810 is very easy to unlock on your computer (for free of course), there are tutorials on this site