Yes, because then real-world testing comes for free.
If the applications the testers are developing are applications they would be using anyway, or if the testing runs automatically in the background, then by all means let them take the phones home. Or on holiday, or anywhere else. The quality of system testing is roughly proportional to time spent, and the more time spent, the greater the probability of running into one of the (inevitable) corners you've not thought about. Your team don't need to be doing anything in particular, they just need to have the phone with them.
I worked in mobile phones for a couple of years. We were all issued with development phones which we could take home with us, fully equipped with logging. If anything went wrong when we were away from the office, we raised an issue and dumped logs when we got back in. I was working on system-level debugging, so a lot of my work came from these issues. It was incredibly effective, it didn't take time from the engineers, and it only cost the company the price of phones, SIMs and calls.
The most significant case where this helped us was an obscure issue with the phone dropping the network. Hong Kong were reporting this as a regular occurrence, but we simply couldn't reproduce it over here. Then a team leader happened to go to the local pub near us, and found that his phone fell over repeatably with exactly this fault. This was the first time anyone had managed to get it to happen anywhere in the UK. So my friend talked nicely to the landlord, and for the rest of the week his entire team relocated to the pub, occupying a fair chunk of the restaurant area with their PCs and hardware test kit, until they'd fixed the bug!