Australians are being encouraged to send messages of support to troops serving overseas this Anzac Day, with $1 donated to charity for each one that's delivered.

A similar scheme last year resulted in almost 40,000 messages being delivered to Australian Navy, Army and Air Force personnel, raising a smile among many serving abroad.

Telstra, which is running the scheme, will donate $1 to Legacy, a charity that supports the families of dead or injured servicemen, for every message sent.

The telecom giant has capped its donation at $20,000.

"Many of the men and women of the Navy, Army and Air Force spend long periods of time away from family and friends," Chief of Defence General David Hurley said.

"Whether it be protecting our borders, assisting in disaster recovery or service abroad, these messages will reassure our people that Australia is behind what they are doing and appreciate their work."

Messages can be sent via 0447877678 or online at telstra.com/anzacday until 5pm (AEST) on April 26.

Telstra said it will collate the messages before distributing them to defence personnel around the world via secure channels.