Are my tweets getting read?

I've been tweeting a semi-celebrity, and when I read their @'s (incoming tweets to them), my tweet hasn't been showing up in their inbox, or it at least doesn't show up on the @ list. Wtf? I've been tweeting from my iphone btw, and the past couple of times I've looked my tweets haven't been coming up? Are they still able to receive them even though they don't show up there? I even looked on twitter using my computer, so I can't see them on the web or mobile version of twitter...