In order to use twitter via phone, you either:
a) surf the web via the phone and tweet like you normally would (iphone and similar phones have apps you can use to do that)
b) do it via txt message; which is what I do. Twitter has instructions on how to set it up. Basically you add your phone # to your account and they send you a test message, then you go from there.
[I opted for not receiving tweets by txt since it's a lot and I don't have unlimited texting but everyone has different preferences]
You do not need to add @ when you tweet, unless you want to refer to someone or say something to someone. If you want to send me a msg, you'd tweet "@liesl78 Good morning!".
If you want everyone to see it, simply tweet "Good morning!"
We use the hashtag #BringSeanHome when tweeting about Hague/Abduction cases.
Example: "Please ask your congressman/woman to sponsor HR3140 & HR1326 #BringSeanHome"
The hashtag enables you to click on it and see all tweets that used the same tag.
Did I answer your questions? :-)