I see cell phone shops everywhere, but where is the best place to buy a phone? I know prices depend on their current mood, so I was curious to know people’s experience on the matter. Not looking for anything fancy, just a simple # to relay voice calls.

There is no real best place if all you need is a cheap phone to relay calls (whatever that means). I would just buy a cheap used phone from any of the booths at Tuk Com.

Alternatively, if you're worried about being overcharged/ripped off just go and buy a simple Nokia brick from Tesco for a princely 600THB.

Look in Tesco ads in the Thai newspapers, usually see ads for basic Samsung or Nokia phones at around 600 Baht - buy one get one free!! Basic phone only, no camera etc. Or inside Tesco, Nokia C100 (i think) basic dual sim at around 999 Baht!