Well Im in a country where you can really only buy the Pearl or Curve and they cost a small fortune.
I was thinking of buying a BB Red Curve of Ebay unlocked... is it possible to just pop in my usual BB service simcard here and it will work??
yes. any unlocked phone will accept a SIM card from another carrier. just go on your current carriers BIS site and switch the new IMEI and PIN onto your account to complete the setup.
The curve's are great devices, they are the most popular devices ... beating the iPhone! Read article here.
And to answer your question about whether it is old or not ... os 4.5 is definately reaching its prime and newer devices like the pearl flip, 8900 and bold are taking precedence.. and this summer is going to be one h*ll of a summer for RIM, as they are going to be releasing many BlackBerries. So my advice to you would be to probably wait it out a bit, if you are looking for a lost cost solution to get the best of Blackberry, you can go for the pearl flip 8220, or wait it out for the gemini 8520 which will be the new generation of curves.