Complete mess with iMessages and SMS messages and different devices.....help I wonder if anyone on this amazing site can help. I have an iphone (have had for years). Recently it went automatically to 'blue' imessages as default.  This caused problems as it requires me or the receiver to be in wifi range for messages to be delivered, so I disabled it on my phone. So now all my messages sent are GREEN sms messages via the mobile telephony system (i.e. normal). These are free to me as included in my monthly contract.

Now the challenge - I think that OTHERS' phones are defaulting to iMessage when sending to me, but obviously not arriving with me as I have disabled iMessages.  Instead, it looks to them that the message has been sent to my phone - but the message then delivered to my iPad (which largely resides with my daughter now) as this has iMessage.  

So the problem is this: how can I keep iMessage on my iPad (which could be useful sometimes) and NOT deregister my phone number with AppleID (as it may be useful somtimes when travelling to turn iMessagess back on) BUT make any attempt to send me a message to my telephone number go via SMS telephony rather than iMessage. The only solutions I can see would require them to turn off 'iMessage' default, but that is not do-able. At the moment, both sides (them, sending messages which look like they have been safely sent, and me, scratching my head about the lack of response to my SMS texts to some friends) are left in the dark.  It's not even as if the sender realises it hasn't arrived - the message simply goes to my iPad instead.

As I see it, at the moment, Apple has behaved very badly indeed in making the old system incompatible with the new one they are trying to establish, and making it impossible to set a 'first try iMessage then do SMS if there is a contract and the message has not gone to the phone number via Wifi'condition.  They are essentially making life difficult for people to move from iPhones, but in this case I even have an iPhone and simply want others to be able to text me in a way which gets through. 
Any ideas? Is anyone else affected by this?
Use this apple self help tool to de-register your phone number from iMessage.  At that point Imessage will still work with an email address.  But you can't have it both ways, the problem you are encountering is that other phones ask the apple server if you are reachable by iMessage and if you are thats how the messages are routed.

You didn't ask, but you shouldn't need WIFI for iMessage to work correctly.  If it does not then likely you have changed carriers and kept the same number.  If that is the case, log out of iMessage on all devices, de-register the number with the above tool, and then re-log in, letting your number get registered.