Three has abolished roaming charges for customers that visit the US, Indonesia, Sri Lanka and Macau, as part of the expansion of its Feel At Home scheme.
The company became the first mobile operator to abolish international roaming charges for UK customers travelling to seven countries with the launch of Feel at Home in September.
High roaming charges stop people enjoying their phones while they're away.
The scheme allows customers to draw on their data, text and call allowances while using their phones in certain countries, avoiding costly roaming costs in the process.
Dave Dyson, chief executive of Three, said the scheme means customers no longer have to curtail their use of mobile devices while overseas.
"We want customers to get the most out of their devices at home or abroad. High roaming charges stop people enjoying their phones while they're away and Feel At Home is the antidote to that," said Dyson.
"Adding the USA to the mix is great news for our customers and shows our commitment to giving them the best experience in what is a popular destination. We plan to add more countries to the mix soon."
The company has credited initiatives like Feel At Home for enabling it to achieve a 9.7 per cent year-on-year rise in the number of active customers signed up to its network since Q3 2012.
Three says it has 7.8 million active customers, 300,000 of which joined the firm in Q3.
Richard Woodward, chief financial officer, said the growth of its subscriber base has resulted in another quarter of improved profitability for the firm.
"With a strong network foundation in place and a growing brand reputation, we've seen another quarter of improving profitability. We have also continued our customer growth in both the contract and prepaid markets through simple and enjoyable propositions like Feel At Home," said Woodward.
"With nearly eight million customers now on the Three network, this is an excellent platform to continue to grow our financial performance."
The operator will be hoping the start of its 4G rollout plans, which began in earnest this week, will have a positive impact on its future financial performance.
The firm started upgrading customers with 4G-ready devices to its superfast network earlier this week, and said it hopes to have completed this stage of the deployment by the end of Q1 2014.
To achieve this, it has already vowed to cover 50 cities with 4G by the end of 2014, and 98 per cent of the population by the end of next year.
"We are building a brand and network that encourages and enables customers to enjoy the mobile internet," Dyson said.
"Customers are using more data than ever on Three, far more than on any other network. As we add 4G capacity to the network, this experience will only get better."
