Here's an interesting, if somewhat unusual, approach to helping customers: European mobile service provider O2 is rolling out a "Tweetserve" program to provide assistance to users on Twitter. Once you've followed @O2 and tweeted "#TweetServe" at the company, you'll be followed back and receive a direct message with a verification code. Send that PIN to O2 via SMS, and you're now able to DM the company with nine preset hashtags, including #charges, #minutes and #offers as well as #android, #windows or #ios (for info on software updates).
The #charges and #minutes commands, which show your current bill and remaining minutes, respectively, look to be the most helpful. If you have a more complicated query about your account -- such as a billing dispute -- we imagine Tweetserve isn't going to replace a phone call to customer service. The program appears to be available to users in the UK for the time being; click the source link for more info.