It depends on your mobile phone plan.
Following on Twitter simply means you're are watching for updates on a certain person's account. When two people follow each other, they can send direct messages as well.
If your tweets are protected then only people following you can see your tweets. If she isn't following you then maybe she has access to an account that is following you.
You can use Direct Messages (DM) to do this. However, the person you want to DM must be following you.
He can't reply to everyone or read everyones messages but he does as much as he can.
Twitter is like myspace or facebook. You can follow people's updates. Say if Selena says 'Just finished picking out the picture for my album' if you are following her you can see that she wrote that. You can either reply or favorite the update or none. If someone is following you and you are following them you become friends and you can send messages to each other.
No. Only people that person is following are the ones from who she gets updates. If you mention the person's username preceded by an at, your tweet will appear at the user's mentions page.
liers.
As of March 17,2011 8,202,406 people are following him on twitter
Twitter can be used for chatting. The way it works is that everyone in the chat is using a certain keyword (called a hashtag) in all their tweets. The applications are then grabbing all the tweets with that hashtag from Twitter and displaying them for the people who are part of the chat. Be careful though because your tweets are also going out to all the people who are following you.
no because police and FBI can get into it. Also hackers.
At the top right hand corner it tells you how many people you are following and how many people are following you. If you click on those that are following you, they are in order of when they started following you. So, the one at the top is your most recent follower.
To send messages and follow people, yes, you need an account.