HOW MUCH IS TWITTER?
Twitter is a free service; we do not charge you to use it, even via SMS. However, if you use Twitter via text message on your phone, your mobile carrier may charge you for those messages according to your service plan.
      - Twitter Help Center
ADVERTISING : TWITTER

Twitter offers three types of advertising options – promoted tweets, promoted accounts and promoted trends. The first two cost between $.50 – $4.00 per engagement, and promoted trends will cost you $200,000 per day. Promoted tweets are exactly that – tweets you have already tweeted that you wish to promote.
TWITTER : INFORMATION
If you choose to create a Twitter account, you must provide us with some personal information, such as your name, username, password, email address, or phone number.If you provide us with your phone number, you agree to receive text messages to that number from us. We may use your contact information to send you information about our Services, to market to you, to help prevent spam, fraud, or abuse, and to help others find your account, including through third-party services and client applications.
PRIVACY POLICY
Privacy Policy describes how and when we collect, use and share your information across our websites, SMS, APIs, email notifications, applications, buttons, widgets, ads, commerce services, and our other covered services that link to this Policy , and from our partners and other third parties.