My iPhone won't send iMessages to iPhone users?

I've been having this problem frequently, like everyday now, and my phone simply will not send an iMessage to any iPhone users! I've tried really hard, resetting it, deleting the network settings, and everything. And yes, iMessages is turned on. Like 500 times, I've had to turn it back on. It just sends out as a regular text message! I text a friend in Norway regularly and I know it has to cost for regular text!

Does anyone else have any other ideas?

Added (1). I'm the only iPhone user in my house. My mom and my sister both have regular phones. And even if they did have an iPhone I'm on my own iTunes account.

Added (2). And whether they have an iPhone or not, it's supposed to go out as an iMessage unless they have the SMS option turned on, where the message goes out as an text if iMessage isn't available. I said that its been happening everyday to me, and even if I turn iMessages on, it turns itself back off.

Make sure the other people who have iPhones are also iMessage users, if they are not, or if you are not, it will send as a regular text message. Also make sure that you have the iMessage feature turned on in settings, so that it will send iMessage to other iPhones (with iMessage on theirs of course).

I second that

  • Why won't my iPhone send messages to non-iPhone users? I've had my iPhone 4 for a while now, I go through Virgin Mobile. I've never had problems until recently, but it's really strange. I can text certain people with non-iPhones, but some I get an error. I can receive theirs always. Any resolutions? I have changed the contact from iPhone to just mobile… Still doesn't do the trick. I have turned off MMS. No such luck.
  • Why won't my iPhone send iMessages? I have an iPhone 4S and my friend has the 5. She kept the same sim, so when she got her 5, the old messages from her blackberry weren't deleted. But now, our messages aren't sent through iMessage and its really annoying. Any ideas how this could be put right? All my other friends that I message are sent on iMessage, just not her.
  • Why won't my iPhone send iMessages to other iPhones? I can use iMessage on my iphone4 with no problems at all to iPods, but not to my partners iphone4, it always defaults to SMS. Its frustrating, because we live in an area with poor mobile coverage, so if I need to message him urgently, iMessage in theory should be the best way of doing it. Does anyone know how I can alter this please?
  • Why won't my iPhone 5 send iMessages anymore? It's an iPhone 5 I got in February and it won't send iMessages anymore and yes I'm sure I'm sending the messages to an iPhone and my cellular data is on.