This is usually a problem with your (or the recipient's) cell service provider. Try sending to other recipients that use a different carrier if you are aware of their carriers. If this is a problem with iMessage then it would not be a problem with cell providers unless you or they don't have data connections.
Comments
This is usually a problem with your (or the recipient's) cell service provider. Try sending to other recipients that use a different carrier if you are aware of their carriers. If this is a problem with iMessage then it would not be a problem with cell providers unless you or they don't have data connections.