Strictly speaking, no.
iMessage, a new app launching as part of iOS 5, will offer iPhone, iPad and iPod touch owners unlimited free messaging over Wi-Fi and 3G networks.
The New York Times reports that the forthcoming service is being perceived as a threat to mobile operators. iMessage and other similar services will allow smartphone users to rely on existing data plans and Internet service for text messaging functionality, thereby avoiding having to pay for high-margin SMS plans from wireless operators.
SMS, MSS (photos, etc) are supposed to work in iMessage. HOWEVER…. iMessage only works with iOS devices and Macs. Ohhh… So close! So if you send a lot of texts to non-iOS users, you may still need a SMS plan. That or WhatsApp (hint-hint).
UPDATE: If you have installed iOS 5, you may be wondering where the mysterious iMessage app is? Well, the Messages app is iMessage. Or more accurately, the Message app uses the iMessage service to send free messages.
One thing to keep in mind is that your SMS service will be used as a backup is iMessage is not available. So, if you cancel your SMS service, you may get surprise in your monthly bill! Fortunately, you can set up the iOS Message app to only use the free iMessage service (instead of SMS through your carrier).
To do this, go into “Settings” then “Messages” and toggle “Send as SMS” to “OFF”.
Now you can sms all your iOS colleagues without running up $0.20 to $0.30 per message charges.