UK iPhone carrier O2 has teamed up with micro-blogging service Twitter to turn Twitter updates into free text messages for @ replies and direct messages.

From the start of August, every O2 customer will be able to switch on text notifications within Twitter and receive replies and direct messages for free. They will also be able to send updates to Twitter as part of their normal text message bundle or for the cost of a normal text.

O2 already has similar partnerships with social-networks Facebook and Bebo. O2 is the exclsuive carrier for the Apple iPhone.

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Once switched on, replies and direct messages will start to come through by text throughout the day, although users can choose to turn them off at certain times if they so wish.

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O2's fair use policy for Twitter texts places a limit of 600 messages per month.

Users can switch on the service in their Twitter settings from August 1.

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"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," said Antony Douglas, Head of Content at O2.

"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."

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Vodafone allowed its customers to text 'tweets' from their handsets at the end of March 2009. Its users could create an SMS with their tweet and then send it to 86444 for their Twitter profile to be instantly updated.

Vodafone also allows users to receive text messaging with updates and @replies from the Twitter members they are following by simply turning 'Device updates' on or off, underneath the member's name in their followers list.