I believe the Galaxy Tab gt-p6800 is the GSM version while the SCH-i815 is the CDMA (Verizon) version. Cases are the same for both.
Not exactly true. The verizon version has the IR port where the GSM version doesn't. Cases made specifically for the GSM version might cover the port.
That being said, I like minimalist cases and the Samsung case (available from verizon online) is pretty nice. Very thin and minimalist which compliments the tablets thin design. A bit pricey at $50 though.
UPDATE: after further checking, the GSM version DOES appear to have the IR port as well. Perhaps the case I saw just covered it up as an oversight.
The Verizon model doesn't have and earpiece and I suspect the international model has an earpiece to make and receive calls according to pictures and specs. This is important when ordering screen protectors and folio cases.