When Twitter decided to shut down its UK operations last month blaming the crippling per user cost, the obvious question was raised: why not convert it to a premium rate SMS service and have users foot the bill? After all, that’s what a number of opportunistic start-ups such as Zygo have jumped in to offer disgruntled ex-Twitter users.

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But Twitter co-founder Evan Williams told TechCrunch UK that while they had considered going premium rate, they didn’t believe in the end that users would be willing to pay the “hundreds of dollars a month to maintain the activity they were doing.”

Williams: “If you get a message from a friend, that’s worth a lot, maybe that’s worth a quarter or ten cents to you. While Twitter may be worth a lot to you in aggregate, the per tweet value really isn’t the same. It’s a different type of proposition. It’s the same with sports scores, or stock prices that people are used to paying premium SMS for. Twitter’s not the same thing. You got to look at how much would it really cost, if the cost is based on getting a personal message from friend. It would be hundreds of dollars a month to maintain the activity they are doing, and we just didn’t think people would pay for that.”

Apparently, the UK’s heaviest users were using the service to send news feeds and direct messaging from the web to their phones, all of which Twitter was paying for. “We extrapolated out, and if we were to get ten times more popular in the UK, that’s where all of our money [would have gone] in six months,” said Williams.

Surely, though Twitter must have realised this before they launched in the UK, where it was always clear from the start, that British mobile phone users do not pay for the SMS they receive, as they do in the US? Williams noted himself that the UK service was “ridiculously expensive for us and always us and we knew it wasn’t sustainable.” But the company had been prepared to pay up as long as the usage was manageable, but with Twitter apparently growing faster in the UK than the US, it was ironically time to shut down.