This we assume is a concept music phone that comes with stereo speakers.
If it means you can have more devices for less money, and interchange between the ones you need most in certain environments, we think Modu is on to a real winner.
The real test will be whether the modular pieces are comparable to their standalone competitors. There's bound to be some trade-off in performance for the versatility and low price, but there's simply no point if the 'jackets' don't function at a reasonable standard.
Update: We got our hands on the Modu phone at the Mobile World Congress in Barcelona. Click here for photos of the Modu phone in person.