This article has been updated to add comment from T-Mobile.

MetroPCS is urging customers in Las Vegas and parts of New England to upgrade their handsets to T-Mobile HSPA+/LTE models by June 30 as the legacy network in those markets is shuttering June 30.

“We are not shuttering service for MetroPCS customers. We are moving MetroPCS 3G CDMA customers to a better, faster network and offering them 4G HSPA+/LTE phones– giving them a better experience on a better network at almost no cost to them,” a T-Mobile spokesperson told Wireless Week.

A page on MetroPCS’s website, spotted by Phonescoop, highlights Las Vegas as well as Boston and Hartford, Conn as the first markets to see the changes.

T-Mobile/MetroPCS is offering a free phone upgrade for some device trade-ins—for example, a MetroPCS LG Connect can be traded for a T-Mobile LTE-enable LG Optimus F6. For older phones still running on MetroPCS, the company is offering upgrade credits of $29, $49, $99 or $199.

For MetroPCS customers still on the legacy network in other markets, the carrier warns that using those devices in these markets after June 30 could result in limited MetroPCS service and possibly incur roaming charges.

Speaking in March at an investor conference, T-Mobile CFO Braxton Carter said the carrier plans to have the “vast majority” of the MetroPCS network shut down by 2015. T-Mobile intends to use MetroPCS’s spectrum in its LTE network, including deployment of 15 x 15 MHz and 20 x 20 MHz LTE in some markets.