This Emirates service is complimentary, but the mobile service provider you are connected to may apply their own charges. This depends entirely on your mobile network, however email alerts will always be free of charge. View the list of providers here(Opens a PDF in the same tab).
In order to sign up to receive alerts, you must be the owner of the email address and/or mobile phone, or a lawful user of it who is authorised to incur any charges that may be applied.