Telstra has flagged significant increases to international call rates from prepaid mobile phones on its network.
The telco had begun notifying prepaid users of the changes, which come into effect 2 August.
Some common destinations, such as the United States, faced a small increase - from 66c to 99c a minute - while others, such as New Zealand, nearly tripled from $1.22 to $3.49 a minute.
Trans-tasman rate hikes came despite calls for an inquest into roaming rates between Australia and New Zealand.
Calls to more uncommon destinations faced steeper rates of up to $11.99 a minute under the revised plan. Previously they cost about $4.40 a minute.
A Telstra spokesman said the rate changes brought the telco into line with its competitors.
"We haven't increased our base pre-paid IDD voice rates for 10 years and the cost of doing business has increased significantly in that time," the spokesman told iTnews.
Call connection fees also increased and international calls would now also be charged in one minute - rather than 30 second - blocks, a move the telco has previously applied to home phones and local prepaid calls.
The new plans did see some positive changes on the costs of messaging international numbers.
There was a drop in international SMS rates from 50 cents to 35 cents a message, and the cost of MMS and video messages to international numbers remained steady at 75 cents.
How Telstra compares
Although Telstra could boast cheaper SMS rates, international call rates from local competitors were cheaper.
Connection fees for prepaid users on Vodafone's network varied between 15c and 39c (the latter putting it on par with Telstra).
Users could pay as little as 20c to 80c a minute for most destinations on a specific international prepaid plan; other prepaid plans such as the Flexi caps pegged the costs for most countries between $2.20 and $6.00 a minute.
Optus, likewise, offered a flagfall of 39c for all international voice calls from prepaid mobiles, and charged between 49c and $8.44 for most destinations.
Low-cost MVNO Lebara offered offered a 25c flagfall and standard prepaid call rates of 39c a minute to uncommon destinations such as Afghanistan.
Telstra's spokesman said prepaid users could make international calls as part of the bonus calls Pre-Paid Cap + users received. Bonus values ranged between $220 for a $30 recharge and $940 for a $60 recharge.
"By increasing the IDD costs we can continue to be generous with Bonus Credit which can be used for many, many things," the carrier's spokesman said.