Yes, My g/f & I both have iPhone 4's... iMessage gave me errors saying cannot send message. But, when she used it, hers worked sometimes. I just chalk it up to overloaded servers (even this discussion site is turtle slow) &/or haste to get this feature into iOS 5... I personally don't care, we both have Unlimited worldwide texting plans & aren't too excited about messaging programs. We just turned the feature off.