Some help on what the letter i in front of someone's first name means?

It's used to call pets or close friends, even sons. If the dog is called X, then you would call "I X yoo nai" or when talking about more than one dog, you could say "I dtua yai" if you were talking about the bigger dog.

In Isaan, a common name is "I ham" and then you add "nori" or "yai" depend if he is older or younger.

So basically, it's used in the informal way as a particle to used in front of the name. Stay away from it, unless you know when to use it correctly.

N.B hope you understand the pronounciation, ThaiVisa won't let me post in Thai script from the iPhone or iPad.

อ้าย [long vowel, falling tone] is used only with males (whether human or pet). Rather confusingly, it can be an honorific, or used talking to someone of lower status (e.g. master to servant), or between close male friends.

ไอ้ [short vowel, falling tone], however, is used primarily with pets, and is a sign of affection. But when it's used before a person's name it's a very crude insult.

ไอ้ [short vowel, falling tone], however, is used primarily with pets, and is a sign of affection. But when it's used before a person's name it's a very crude insult.

Here is why you have to be careful with the use > definitions

As I wrote in one of the now locked duplicates of this thread, there are enmtries on thai-language.com:

It is either ไอ้ [F]ai or อ้าย [F]aai. It probably indicates a significant lack of indifference towards the person.