Why won't my iPhone 4s let me text non iPhones?

I just got an iPhone 4s for my birthday a few weeks ago and it was working pretty swell then I updated it to its newest version, I think iOS 8.1, but after I updated it, it won't let me text anyone that doesn't have an iPhone. Does anyone know why? Or how I can't fix this?! I text my dad on a regular basis and it's hard too now because I have a texting app specifically for him.

Settings and than messages! It should let you turn on. At the bottom is should say turn on

  • 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 Iphone 6 ios 8.4 won't deliver text to non iphone user? My iphone 6 (ios 8.4) won't deliver texts to someone who isn't on an iphone. I have tried powering off, rebooting, resetting network settings, turning off imessage and more but i still can't send her messages. However I can still receive all messages from her for some reason?
  • Why isn't my iPhone letting me text other phones (non iPhones)? When my phone isn't paid I noticed I could still text like usual but only if IIm connected to the Wi-Fi, for some reason now all it says it message not deliverd when I text someone without an iPhone but when I text someone with one it sends automatically.
  • Why can't I text non-iPhone? I just got the iPhone 5 today and a lot of my friends don't the iPhone. When I tried to text them it says not delivered. But I can call them. How can I text them?