When my boyfriend started at Uni, I couldn't help but get a little jealous. I admit it now, I was probably quite nasty- however, I never put the phone down on him and, as far as I'm aware, I never sent him any nasty texts. I would just cry, which was very wrong of me as it probably made him feel awful.
It's going to be tough on her- of course I'm going to try and see it from her point of view as well- but she can't really get away with being hurtful to you. You quite clearly love her very much, and it's not fair of her to send you nasty messages.
To be honest, you need to bring it up when you're together face to face. You say everything's perfect when you see her, but if it's this bad then you need to discuss it when you are together and everything's fantastic. I know it might spoil things, but talking is the key thing here, and just explain that she's hurting you with her messages and the fact that she hangs up on you. If I did that to my boyfriend I would immediately phone back in tears begging him to forgive me- sad, I know, but I would regret it as soon as I did it.
People have arguments, but you need to get this sorted now because obviously it's going to last a few years. I take it she's a year younger than you?