From today, all Australian telcos must alert users within 48 hours when they've used 50, 85, or 100 percent of their data or phone and text allowances.
The three biggest operators — Telstra, Optus, and Vodafone — already send such alerts, usually via text message, but many smaller operators do not.
The universal notifications are designed to help consumers avoid "bill shock" — the excess charges slugged on users who exceed their monthly allowances.
They are the final protections to kick in as part of the Telecommunications Consumer Protections (TCP) Code, which was registered precisely two years ago in response to concerns that customers were being ripped off.
In addition to usage notifications, the code has strengthened regulations on advertising, including limits on the use of words such as "cap", "free", and "unlimited".
It has also standardised billing practices and streamlined the complaints-handling process, with urgent complaints required to be resolved within two days.
According to the Australian Communications and Media Authority (ACMA), which registered and enforces the code, the measures are working.
"The industry has developed initiatives in its code to deliver world's best protections for Australian consumers, which should give rise to a much-needed, much-improved, customer experience," said ACMA chair Chris Chapman, when the TCP Code was formally accepted by the authority in 2012 after being submitted by the Communications Alliance.
"The code is a unique and ground-breaking document by world standards, bringing together best practice protections at all of the touch points in the telco customer lifecycle," he said.
Under the Code, Australia's larger telcos were required to have their spend-management tools in place by September 2013.
The industry ombudsman received an average of 594 complaints per day in the first three months of the year, down from 842 per day in the equivalent period in 2012, before the code was registered.