On 31st May 2017 the US mobile network T-Mobile will launch digits - a virtual cloud based mobile number. This may just change the way we use mobile devices.
It's a mobile phone company that puts your number in the cloud. You could potentially have two numbers such as business and personal tied to the same device. A sales team could all have one number so all their phones ring. You could even have numbers in different countries. You have on-call shift workers that need the on-call number. No problem. Just re-assign the number to their device and you dont have to pass around the on-call phone between staff.
The T-Mobile version still relies on SIMs in phones but that may change with the SnapDragon 835. The 835, which I have written about before, includes LTE on the chip. This means that the chip is pretty much a self-contained phone. All you need now is some software on the device that can have your number programmed in with a suitable mobile operator supporting phone numbers "in the cloud".
Right now T-Mobile US is the smaller of the mobile networks and it's adding this service to ramp up it's consumer offer. However the next generation of mobile chips could mean your number gets personal and you can have it on any phone that is charged in the morning and even that Nokia 3310 left in your desk for emergencies.