Use the browser to connect to m.twitter.com and update your status via that interface. Or just use your browser to connect to the twitter website (www.twitter.com) and use it like you use it on your computer
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Also, if you have a Twitter account, and connect a mobile phone number to the account in the settings, you can then tweet from your phone using SMS text messages, sent to 40404 (in the US).
For smartphones, there are also plenty of applications that can be downloaded. Official apps from Twitter include "Twitter for iPhone" and "Twitter for BlackBerry," but there are plenty of third-party applications that connect to Twitter as well, for all mobile devices.
No, you get them online too at www.twitter.com
You will receive tweets on your homepage from everyone you follow. Unfollow them to not receive their tweets. To stop people seeing your tweets (except from those you approve) you can protect your tweets from the settings menu.
The only way you would receive these tweets is if they are retweets or if you are following them.
You block the phone,
They probably receive so many tweets that it's difficult to find your own.
Yes
By downloading the official Twitter app. You'll then receive notifications when someone tweets you. (providing you have an account)
No they have no way of knowing.
Check your settings. You might only have it set to text when a certain user tweets.
Yes, they will appear in their @replies tab.
To not receive tweets from someone on your homepage, unfollow them.
By downloading the free Twitter app. You can then send and receive tweets.