From the start of August, all O2 customers can switch on text notifications within and receive @ replies and direct messages as text alerts on their mobiles, at no cost.
Subscribers can receive a maximum of 600 alerts a month.
O2 customers will also be able to update their Twitter status via SMS for the cost of a normal text.
The mobile operator also has deals with Facebook and Bebo.
Antony Douglas, head of content at O2, said: "We believe that mobile will soon become the most popular way of accessing social networking sites, giving real time access to tweets and status updates wherever you are.
"The agreements we now have in place with Twitter and the other key sites brings this a step closer, making it quick and easy for O2 customers to access their favourite social networks straight from their mobile."
O2's deal with the micro blogging site is similar to one made by Vodafone, which became the first UK operator to give its subscribers free Twitter updates in March.
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