There's a big section on the page devoted to these points, but the main reason is this:

We aren't designing a phone, we're designing a device that allows hardware and low-level firmware hackers to do the things we want to do with phones, but can't due to being effectively locked out of modern smartphones.

That said, it should work perfectly fine as a home or office phone, or as a light-duty mobile one.

Longer reply here: http://a.wiphone.io/#but-i-need-my-gsmcdmalte

Not requiring a service subscription is one of the selling points. Additionally, there are no open-source cell basebands and they all allow your carrier to track you.

They have a pretty good answer for this [1].

Basically, it's a black box component that introduces privacy risks and requires service plans.

[1] http://a.wiphone.io/#but-i-need-my-gsmcdmalte

I wonder if anyone is working on an open source baseband processor? I'm led to understand that existing parts are a mish-mash of documented protocols and "hacks" that are needed in practice to make it work, so I suppose it's a difficult task.

What is cheap? I see some modules on aliexpress for about us$20 but with very limited bands... And I wonder if patent fees are being for those.