Fast-growing US carrier T-Mobile's latest plan to woo customers away from other mobile networks is perhaps its most headline-grabbing yet. Starting on June 23rd, T-Mobile will lend you a top-of-the-line iPhone 5S for free, for seven days. T-Mobile thinks its new scheme, called "Test Drive" and announced at its "Uncarrier" event today, will be used by more than 1 million people in its first year.

The Test Drive scheme is targeted at customers of other US carriers who aren't sure if they can justify switching to a smaller network with less countrywide coverage than its larger rivals. Interested parties can sign up next week on T-Mobile's site. The carrier says people will receive their borrowed iPhone 5S "a few days later." During the week-long trial period, the iPhone will offer unlimited text, data, and calls, as long as it's used inside the US. Users who damage their borrowed phone will be charged a $100 fee.

The phone must be returned in 7 days or users will be charged $700 plus tax

Apple are providing T-Mobile with the iPhones for the Test Drive promotion free of charge. Speaking at his company's Uncarrier event, T-Mobile CEO John Legere said his company had a "growing partnership" with Apple, but that there was still "low awareness" among consumers that the carrier offered the iPhone.

People who do take advantage of the offer won't be able to keep their Test Drive iPhone if they do choose to join T-Mobile, as the service and account will be suspended once the week-long trial is complete. Instead, they'll have to return the device to a T-Mobile store, where it will be refurbished and reset as part of a pool, before being sent out for the next Test Drive user. They also won't be able to make off with the iPhone: people taking part in the scheme will have to return the device within seven days or face a $700 (plus tax) charge.