Let me present two scenarios for you: Scenario 1) Texting works exactly as you are used to right now, this instant. Every text you send or recieve counts against your text plan. Scenario 2) Texting works exactly as you are used to right now, this instant. Half your text messages are now free. As you might have guessed, scenario 2 is with iMessage enabled. There is absolutely no reason, whatsoever, why a sane person would choose scenario 1 over 2. There are no drawbacks to using iMessage, no differences, no costs. It's a gift from Apple, treat it as such.