Rather than a phone call, I am for having your mom or dad take you to their home and walk up to the door with you.
I say that for a couple reasons:
1. You don't know anything about the people - anything. Parents have a very handy "third instinct" that generally isn't wrong. The owners may be the type of folks your parents would feel completely comfortable with having you visit their barn alone -- or those proverbial Bells and Whistles may start going off and your parents might be uncomfortable and tell you to not get involved.
2. Assuming they are very nice people --- were it me, I would prefer someone come to my door and ask with their parents.
I am the type of person that I want to know where your parents are. If they can't come with you for something like that, why not?
Do they understand the dangers of going into a barnful of strange horses? If you were to get hurt on my property, I would not want to be giving permission for someone your age to be around and work my horses if I thought the parents were "Sue Happy".
I think you have a magnamonious idea and it has the possibility of being a win-win for everyone. Just as long your parents have met and spoke with horse owners and everyond understands the ramifications of accidents
I am not trying to be a naysayer but that's what happens when you ask such a nice question and someone that is 65 years old give you their two cents