Text to Speech SMS on iphone. Please Help!!!

Hello, I am looking for an app or feature where I can listen to my sms text messages instead of reading them due to poor vision. I have the iphone 3g 4.2.1. I was told the 3gs has the feature I'm needing. I was told about Vlingo but I dont think it does what I'm needing on listening to text messages. I've found many speech to text apps but no text to speech app, features. Can anyone help me? Again I'm needing something that will talk out my incoming text messages. Thank you very much if you can help me.

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