Hong Kong version of iphone3g can't send short messages. The network signal is getting weaker and weaker. If the message disappears, restarting or canceling the sim card will not work.

I'm using an Apple phone, too. I've had the same problem you mentioned. Maybe it's your card. Some Apple phones may be specially made by Unicom. Using a mobile card will cause many things in the mobile phone to be unusable, and short messages will also be disturbed. According to you, there are several reasons why you can't send text messages: the signal is not good because of the inappropriate mobile phone card, and your mobile phone is loose inside, so it needs to be repaired.