For several years, I carried two phones and a pager. Then one day, my employer gave us all new shiny Blackberries. This was a while ago. We were told we could use the Blackberries for unlimited personal use. Of course, the email was still censured at the server. It was a deal with the devil. After giving us the unlimited use Blackberry, we were never allowed to complain about constant off-hour calls. The "free" Blackberry came along with off-shoring to India and European expansion. This extended your exposure to phone calls to nearly around the clock. Of course, refusing the Blackberry was not an option. I left that company not soon thereafter, not on my own volition, but all things considered, I am far better off away from there.
@hihosteverino, your internet is basically your "commute" cost, which you are saving by not physically commuting to work. If the company pays for it, they will give you a VPN router, and (attempt to) restrict your web access, just like at the physical office.
PHB's answer should be: "I don't know, why do you need to carry your own personal phone?" (Especially on the clock.)
The real explanation usually has to do with tax. And administrative simplicity. While companies often provide a company phone and turn a blind eye to employee usage of the phone, without requiring the employee to reimburse the employee for their own use of it, that's strictly a taxable benefit to the employee. Other companies basically tell the employees to use their own phones, and compensate the employee for their business use of the phone...but that's not ideal either, because it undermines the value of having company-issued phones in the first place.
I've seen far more absurd practices than people carrying two phones.
Yeah, I know, it's a comic. And time-traveling chimps are funny. Call me a killjoy.
I have two phones as the work one is tied down such that you can't install anything on it. Whne at work it is with me as I am often not at my desk. The only time it goes hoem with me is if there is something really important going on or I am going on a business trip. They pay me to work when I am at work not when I am home.