Sprint launched a 30-day trial offering as it pushed its HD Voice service across the US and expanded its LTE coverage.

The struggling number three US operator is looking to win back customers it has lost in recent years by allowing consumers to try its upgraded network and services.

If consumers are unsatisfied, the cost of the phone will be refunded and they won’t be charged a service fee. The trial will be offered to new customers only from 27 June.

The move follows the launch by rival T-Mobile US last week of a seven-day ‘test drive’ for the iPhone 5S on the operator’s data network.

T-Mobile US CEO, John Legere, who has been touting T-Mobile’s ‘uncarrier’ approach, said “buying blind” was another industry pain point that could only be addressed by his company’s new way of thinking.

Consumers who decide to take the test drive can use unlimited data on Apple’s flagship iPhone for a week. If they don’t want to continue with the device or T-Mobile after a week, they can drop the device at a store with no obligation.

In addition to the trial offering, Sprint launched LTE in 28 new markets, including Seattle, Cleveland and San Jose. It also added Sprint Spark, its high-speed LTE service which combines 800MHz, 1.9GHz and 2.5GHz frequencies, in three new markets. Spark is now available in 27 markets and Sprint aims to cover 100 million people with the service by the end of the year.

The operator also plans to launch international WiFi calling in “the coming weeks”, allowing customer to make calls and send texts via WiFi in more than 100 countries.

Sprint has overhauled its 3G network over the past few years and deployed 4G in 471 markets, covering 225 million people. However, the US number-three’s overall network quality remains behind US market leaders Verizon Wireless and AT&T, as well as US number-four T-Mobile US, according to network-quality rating firm RootMetrics.

Though they may be competing at the moment, SoftBank-owned Sprint is believed to be lining up banks to finance a purchase of T-Mobile US, with a merger announcement due in August.

It’s far from certain, however, that Masayoshi Son, SoftBank CEO and Sprint chairman, will convince regulators to allow a merger to go ahead.

Perhaps conscious of the regulatory risks, Deutsche Telekom reportedly managed to secure a hefty compensation package of $2 billion from Sprint in the event that any future merger with T-Mobile US is blocked by regulators.