What are the prefixes before the phone names?

[AC Question]

I always see that some phones have Verizon,AT&T,Sprint etc. names before their model name. What does that mean?

Also, I'd like to buy LG G3 from Amazon but there are so many different products(unlocked,sim-free etc.) that I'm confused. Would you kindly tell me which one should I buy? (I want the 3 GB RAM and 16 GB Internal one)

 

[dpham00]

Can you give an example?

Sent from my Verizon Samsung Galaxy Note 5