NEW YORK (BLOOMBERG) - The danger of getting lost in the desert or stranded at sea, unable to raise an alarm, may become a thing of the past as soon as next year near if billionaire Elon Musk's latest project goes off without a hitch.

The SpaceX chief teamed up with T-Mobile chief executive Mike Sievert to unveil a new service that will utilise Mr Musk's Starlink satellites to offer cell coverage in every corner of the United States.

Mr Sievert said there were a more than half a million square miles of dead zone - areas not covered by any cellular network - across the country, and described the project as "a lot like putting a cellular tower in the sky, just a lot harder".

Here's how the companies plan to do it, what it means for mobile users and what the limitations will be:

What is it?

The two companies want to create an entirely new mobile network, broadcast from Starlink satellites, that uses T-Mobile's existing mid-band spectrum.

The service will give customers that sign up phone coverage practically everywhere in the continental US, Hawaii, parts of Alaska, Puerto Rico and even territorial waters.

How will it work?

The new network will be accessible thanks to large, powerful antennas attached to Starlink satellites.

Mr Musk said each antenna would measure some 25 sq m and be "extremely advanced because they have got to pick up a very quiet signal from your mobile phone and then be caught by a satellite that is travelling 17,000 miles (27,359km) an hour".

The T-Mobile service will run in a similar way to data roaming, where a user's mobile will scan for service and if it finds none it will connect to the satellite.

Most phones already have the technology built in and no additional equipment will be required.

What are the limitations?

The main issue is bandwidth, which will at first limit the service to text messaging.

The coverage area will be divided into large cell zones, with each zone's connectivity limited to around 2-4 MBs.

Mr Musk said that would allow for some 1,000 to 2,000 voice calls per mobile phone, or millions of text messages, but the service would not provide a substitute for ground mobile stations.

"This is really meant to provide basic coverage to areas that are currently completely dead," Mr Musk said.

In addition, he said there could initially be a delay of "half an hour, maybe worse" for messages to pass through the system.

How much will it cost?

Mr Sievert said he hoped that the service would be bundled for free on T-Mobile's most popular pricing plans, while lower cost plans where it is not included could be charged a monthly fee.

Will the service be available outside the US?

It is not clear yet. Mr Sievert said T-Mobile was seeking reciprocal roaming deals with carriers outside the US, "so that when those people come and visit the United States and go off the grid into the national parks, they'll be connected too. And likewise when American citizens travel to those countries, they'll be connected".

What's the timeframe?

SpaceX said in a press release the satellite-to-mobile service would begin with beta testing in select areas by the end of next year, after new satellites have been launched.

Mr Musk said the first phase would include messaging, MMS "and even messaging apps", although he said they had not yet spoken to app providers about how to integrate their services.

What does the future hold?

After messaging, the companies hope to work on voice calls and data. But Mr Musk has grander ambitions.

"We'd love to have T-Mobile on Mars," he said.