Mobile number and email-id are mandatory fields to create an account at the e-filing portal of the Income-tax Dept. E-filing portal requires a new user to verify his mobile number and email-id by submitting the One-time Password (OTP) sent on such mobile number and e-mail ID.
However, it is not necessary to have an Indian mobile number, and you can also register with the mobile number of a foreign country. Dept. will send an OTP to the primary mobile number and primary e-mail id, which you need to enter for creating an account at the portal.