My iPhone 4 won't send messages to people with iPhones (iMessage)?

I can only receive & send messages from people that have iPhones. If it try to send a message with someone that doesn't have an iPhone or iMessage it says "not delivered" & i don't receive any messages with people that try to text me without iPhones.

To send messages to people without iPhones, you need a cellular subscription. Do you have a SIM card with an active subscription installed in the phone? If not, you're limited to just iMessage with other iPhone or iPad owners.

  • Why Won't My Iphone Send Messages And I Can't Call People? So whenever I try to send a text message to someone it never goes threw and when I try to call someone it won't work? Sometimes it will say ''calling -enternamehere-'' but there's no ringing or anything and it could stay like that for hours if I just never hit end call. It WILL work if I turn my phone off and back on though. Anyone else have this problem? Its an iPhone 4.
  • Why won't my verizon iPhone 5 send messages to certain people? I have a friend who has verizon and it sends messages to him very fast and I have friends who have different carriers and it won't send to them. The send bar keeps on going and stops at the last second. I have turned it off and on again and I have reset my network settings. Nothing has worked at all.
  • Why people like iPhones? I can't never get people who like iphones to give a good reason, why? Some say it easy, but a lot have no clue on how to use their own phones. Can someone explain something useful that great about iphone? Everything they think is special other phones have been doing for years.
  • Why can't I send picture messages to people who don't have iphones? I have an iPhone 4 and whenever I try to send pics to ppl who don't have an iphone, it fails. I have data on, 3G on SMS on and MMS messaging on and they still don't send. The pictures are also not in HDR when I take them. Is it because some people who I'm sending them to don't have smartphones? I have everything on that's supposed to be on so I don't understand why they won't send.