Can a 17 year old and a 25 year old text and talk on the phone even if parents of the 17 year old disapprove and can they get the 25 year old in trouble?

Yes, they could. You see, at age 17, you are still a "minor child" in terms of the law. Any normal 25 year old person should not be "preying" upon someone your age. To the parents, this might appear as "stalking" ... Since the parents are most likely paying for that mobile phone and the texting charges, they have every right to restrict to whom and when you text.