Alright, it's pissing me off that nobody is challenging this "Chinese cell phone cancellations = tens of millions dead from the WuFlu" narrative, so here we go:

Like everything else in the Chinese economy, these telecom companies were probably artificially inflating the numbers to look like they had more business than they actually did. The previous numbers were probably fake. Now that the Chinese economy is crashing, they probably can't hide the fraud any longer and are forced to re-adjust to something more believable (but still not necessarily accurate).

Makes more sense to me than "ten million people died and nobody noticed except for the missing cell phone data that is somehow truthful when everything else coming out of China is fake."