Like the BlackBerry service, the Danger client/server platform enables an 'always-on' connection, continuously synchronising, backing-up and managing the secure transmission of data between the network and the device.
The Sidekick II, which is manufactured by Sharp, offers push email, instant messaging and web access.
Phil Chapman, marketing director at T-Mobile UK, said: "It's the ultimate communicator and key to our web'n'walk offering."
Sidekick II will be available at T-Mobile retail stores and online from £30 a month. The cost of the device ranges from nothing to £49.99 depending on the selected price plan.
Danger's marketing efforts ensured that it was used by leading photographers, designers, artists, models and journalists, partly thanks to providing popular designer versions of the phone and what some saw as "engineered" product shortages.
Even the product naming was trendy; Sidekick II was originally called 'Hiptop' and positioned as the youth market's answer to the "stuffy" BlackBerry.
Danger is in the process of developing the Sidekick III for release next year.
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