IFATCA Policy is:

Voice communication is fundamental for the transmission of non-routine messages. Where data-link is available as a means of communication:

• A set of pre-formatted messages is necessary to minimise the need for ATCOs to compose free-text messages;
• ATCOs should revert to voice communication to transmit non-routine messages;
• Whenever possible, Standard phraseology should be used in composing free-text messages.