Telecom customers wanting better overseas roaming coverage and mobile broadband services will soon be forced to upgrade to its XT network. But it remains unclear how much this will cost them.

From October 28, Telecom customers will need to upgrade to the company's XT network if they want more extensive and better coverage for roaming while overseas. They will still be able to use their WorldMode CDMA phones locally although the technology will be obsolete by mid-2012.

EVDO customers that stay on CDMA after November 30 will also be able to use data but will no longer experience mobile broadband speeds.

At the end of March, Telecom's mobile customer base was approximately 2.3 million - this included total texting and calling customers on both of its mobile networks.

Of these customers, roughly 1.7 million customers are on its CDMA network with the numbers of customers using the Worldmode and EVDO services are a very small proportion of the total CDMA base.

Telecom spokeswoman Carly Morris said the company was promoting deals that contributed to the cost of a new XT handset and other offers. She said the offers would vary on what service customers used and whether they had been an active user of the service in the past 12 months.

"In many instances, a new XT handset or data device will be free and in others, customers will be offered a subsidy," she said.

Ms Morris said the majority of roamers and mobile data customers had already upgraded to XT.

"This reflects the fact that XT provides a better data and roaming experience."

Asked if Telecom's XT network could handle a mass-migration of customers without further major hiccups, Ms Morris was confident.

"We have done a lot of work on XT over the past few months and are confident that XT is working as it should," she said. "Simply put, we wouldn't be closing down these services unless we could provide a superior experience and better value for money on XT."

Telecom Users Association New Zealand spokesman Ernie Newman said the CDMA network had reached a point where it was no longer economical and people were embracing newer technology.

"I haven't heard anyone who has felt aggrieved that that service is going to be closed down."

He said XT's recent performance had been "as good as anything". "It's been quite a while since we've seen any problems with it and there's a high level of customer confidence with it right now."