Actually I could use a quad sim phone: for work and personal, and one slot for a data only account, and another slot for a chip that works in my home country.

If you're wondering why someone would want a separate data chip, the best data plan and best voice plan for someone isn't always offered by the same provider.

There are also cases where you get intra-network discounts; so it's useful to be able to access a variety of different networks from the same phone.

I wouldn't mind swapping sims in and out in some cases, if they weren't kept under the battery. A phone that can easily hot-swap sims would indeed be useful, but they don't seem to exist.