- What are the components I need for assembling a hobby mobile phone?
- How would I go about assembling such a hobby device?
- Are there laws governing assembly/use of such hobby devices?
Modern mobile phones are complex, highly integrated devices. I described what would be needed in a previous answer of mine to a similar question. Take a look at the schematic of the Neo FreeRunner phone to see what's involved.
For a very simple phone, you might be able to get away with a GSM module + some other electronics, as in the DIY Cellphone.