SCH-L710 vs SPH-L710


Could someone please explain to me the difference between the Galaxy S3 "SCH-L710" & "SPH-L710" and also, what does "GT-19305" have to do with it b/c I don't see that number anywhere on my S3. When I Google firmware for my SCH-L710 (this is what's on the back of my phone) 95% of the results come back as SPH-L710. Is it just a difference in the cellular network (mine is C-Spire)? Does that mean I can download the firmware for the SPH-L710 even though mine is SCH-L710?
Thanks for ANY help with this!!