This user reports that her husband found out about her secret party due to the issue that anybody can read new text messages on the iPhone:

I love my iphone. HOWEVER, there are two basic functions that this expensive luxury lacks, that my 8 year-old niece has on her phone. Texting pictures and text message privacy. The first is well documented so I won’t go there, but the second is just plain wrong. I have a password on my phone for a reason. If I wanted every Tom, Dick, and Harry to be privy to my text messages I would turn off the password function. But I don’t! It frosts my cookies that if I put the phone down and walk away, anybody and everybody can read any text message I receive right there on the front page!!! I am so PO’d about this!! My husband found out about his surprise party because of this stupid mistake! I couldn’t even get mad at him when he brought me the phone and said, “you got a text message about my party.” What the heck? This is basic! On my old $30 phone, you had to go through dang near 25 screens to get to text messages. AND IF MY PASSWORD WAS ON YOU COULDN’T GET PAST THE FIRST ONE! Sorry for the yelling, but I am really upset about this. Apple, I need you to do better.