Recently Twitter has turned off its Twitter via SMS service with a few countries as an exception. Besides that, millions of inactive accounts created via this service were deleted. The reason for that is that they can easier be compromised, and the service itself has vulnerabilities.
If you have been active on Twitter for the past few days, you may have noticed a drop in following for some accounts. It must have been especially visible for larger accounts.
SMS tweeting wasn’t hugely popular for some time now, so overall, that doesn’t seem like that big of a change.
To find out more about the service, you can go here.