Making a commercial cell phone

I am new to electronics(though, I have decent experience in embedded systems programming).
I have couple of questions.(I probably might sound immature or over estimating myself...but still, I would like to ask)

  1. How difficult is it to make a SIMPLE cell phone (Voice &SMS) with the intention of selling it on retail markets? Mainly from technically, process,approvals and documentation point of view (for example using hw like arduino with some gsm shield). Obviously, budget not in millions of dollars.
    I.e., I am not asking about marketing efforts, usefulness of that kind of product, thinkable market segments etc. Just without considering those for now.

  2. Does the hw suppliers like parallex, telit etc create custom designs for these kind of product orders? For example, squeeze arduino+gsmshield into single small board and preprogram our software. If not, can you give some examples of companies that might be doing this kind of custom designs?

I will be very thankful to all who reply on this with any info.

Thank you

PLEASE do not multi-post...