Alright seriously, stonewalling is passive aggressive. If I call, text, or email a girl and they don't reply, it makes me feel like they're saying "f*** you" or "You're being annoying" and I take it personally or think that there must be something wrong with me. At least say "here's why I don't want to talk to you, or I'm not interested in you" instead of not responding or saying "Oh I'm busy". It's alot more assertive and honest for someone to do that, because if a girl doesn't respond to me, I'm going to take it personally.
I understand that many girls have to deal with many guys repeatedly calling them or texting them and saying "you want to hang out?", etc. and that with such an information overload, it would be troublesome to try to have to respond to every message.
It really is best to respond to someone though, unless the guy is just playing games and being manipulative. Being friends with someone is about communicating with them, and communication is essential for relationships as well.