Default Difference between E975 and F180L

Hello everyone,I'm sorry if I repeat someone's question,but I didn't find an answer....I think of buying an optimus g and I have found that there are more models beside it's name,so I want to ask you if somebody can explain which is the difference between E975 and F180L because I don't want to buy the phone without knowing some details and regret afterwards....thanks in advance)