However, the flat fees did not give mobile roamers a free rein and Telecom said if customers used "significantly more data" abroad than at home, they could get cut off.
The company will also review the $6-a-day deal in the middle of next year, suggesting the price could rise.
New Telecom chief executive Simon Moutter said he "shared the pain" of high roaming prices before he stepped into his job in August and personally pushed his employees to find a solution.
"A flat fee provides certainty and puts an end to consumers' nasty bill shocks on your return home," he said.
"It's also much simpler to follow than any usage-based system, as most customers don't know how quickly their phone apps will chew through 1MB or 10MB or 100MB."
As well as the flat rate prices, Telecom yesterday reduced the roaming charges for pre-paid customers across the Tasman from $4 to $1 per MB of mobile data.
It also cut the cost of calls from roamers in Australia and a string of other countries.
The new prices come into effect on December 21 and while consumers will be hoping for a roaming price war, a Vodafone spokesperson said yesterday the company had already dropped some of its data roaming charges by 70 per cent in October.
Vodafone, New Zealand's biggest mobile operator, has also introduced a service which lets users track how much mobile data they are using while overseas to stop "bill shock" on their return.
Asked if it would respond to Telecom's new plans, 2degrees said it was "constantly reviewing" prices.
"As part of this, we'll certainly be taking a look at these roaming price changes," said 2degrees' chief marketing officer, Malcolm Phillips.
Telecommunications Users Association chief executive Paul Brislen applauded Telecom's move andsaid he was glad that the company was trying something new.
"It signals well for the future that we've got companies trying different things. It's not just a case of reducing the price per MB or per minute. Hopefully we'll see more of it from Telecom and more of it from its competitors," Mr Brislen said.
Trade Me founder Sam Morgan was also pleased with the new plans.
"Fantastic to see Telecom changing roaming rates to be very reasonable. $6 per day data roaming in Australia, $10 in USA. Awesome," Mr Morgan said yesterday on social media network Twitter.