SMS - getting @replies to person I'm following. I don't want this!

Do you think it's possible that you've created a track alert for that person's username? If yes, that would explain why you're getting @replies directed at that person on your phone.

To see a list of all the keywords that you're tracking, send "track" to Twitter from your mobile or IM. Twitter will reply with all the keywords that you've registered.

Another way to check if what you're getting are track alerts is to see if the usernames of other people appear in parenthesis.

For example, if you friend's user name is "john" and I were to send him an @reply, and you were tracking "john," then you would receive a tweet from me with my name in parenthesis.

(mdy): @john, these replies are confusing!

It's possible that there's a different cause for your problem, but this is the first one that comes to mind. If track alerts are indeed the cause of your problem, you can stop tracking your friend's username by sending "untrack john" to Twitter via sms or IM.