Grace

So I have a blackberry torch at the moment and its getting all the normal blackberry problems, and its starting to die. I fell in love with my friends phone, the Samsung Focus. If I buy it off ebay can I just put the sim card in it and it works? And does anyone know where I can buy it for cheap? Yes I know ebay and craiglist but anywhere else? My upgrade is in August and I don't think its going to make it much longer! Please help asap!