Thanks for your prompt and extensive answer.
I checked out samsungparts.com and the only spare part available for the Q3 is the manual. They do have a replacement battery for the Q2 but, as you say the price is exorbitant ($29) and the shipping charge is totalment fou ($29) -- total cost equals the price of a new Q3. Q2 replacement batteries are available on Ebay for $15, so samsung know where they can go with their parts.
However, your advice re the Q2 keypad has convinced me :-) as I'll be playing the unit from my pocket half the time, so I go for the Q3 (macho black version)
Still, I can't help thinking that it's a shame that devices as nice as these don't come with a user-replaceable battery, like a mobile phone.