I will have to say that one thing I've never been fond of is the flip-phone design. Maybe if the flip was spring-loaded or something... I find I have two personal problems with them.
- I can't answer or dial them one handed or as quickly as just a regular candy-bar form phone. Nor can I restow them as quickly.
- I tend to be harsh on my equipment. I used to have a cordless phone of flip-design (old Panasonic thing) and broke it rather easily. My old Nokia 6162 had a flip-cover that was mainly cosmetic (it would still function if you removed the cover) and I would always end up accidently snagging it on something or bending it wrong causing it to fly off. A phone with a functional flip would end up in the repair shop quite often.
Additionally, flip-phones seem overly bulky to me.