The completely out of touch developers and product managers at Twitter are at it again trying to create some way to secure Twitter accounts from automated tools sending out messages or following accounts -- it's part of a bigger problem they've been trying to get in front of for years... the problem is that once again they've failed to even consider how the general developer base uses the Twitter API.
If this were 5 or 6 years ago it would be understandable to try and make individuals somehow identify themselves as unique (like good old Facebook does); the problem is that the Twitter Ecosystem isn't set up the same way as Facebook - a decision which later required the addition of first 'Fan Pages' and ultimately just 'Pages'. A lot of companies, brands, artists, etc adopted Twitter early on because it didn't force them to be an "individual" like Facebook. With this change Twitter is requiring you to associate a single mobile phone number with each Twitter account - which I guess would be okay IF they had some option like 'Pages' in the foreseeable future; but they don't.
So let's say you're ummmm IBM; some developer in White Plains, NY has to associate his/her personal mobile phone number to the account in order to have Read/Write access to the account? Then when said developer gets shit canned they have the keys to the kingdom because their mobile phone is attached to the account? That applies to all levels of corporate interaction.
Enter the developer for hire... They're pretty much out of business since they can only associate one mobile phone number to one account... A good developer probably has dozens of clients; so now they'll have to try and walk their client through associating their account with their cell phone -- that's just a customer service telephone call from hell. The developer community is up in arms, read some of the comments here: https://dev.twitter.com/notifications/new-apps-registration
I'm all for limiting SPAM on Twitter; I've railed against the ability to "buy followers" for years... but this security step is a step in the wrong direction for an Ecosystem that is already pretty well defined with 100's of thousands of developed applications that can't possibly adhere to this method of verification. Time after time Twitter has alienated it's developer base; the people that have truly made Twitter strong -- moves like this have developers and soon end users looking for other easier to use options.