As of November 15, 2012 there are 469.
The dog tags do appear when you melee/knife kill someone in Battlefield 3, you just have to look really closely. See related link below.
You can get it from Walmart or the Pet store like um .. . Pet smart :)
From what I have read the only way that you can get the Haggard dog tag in Battlefield 3 is if you had pre-ordered the game. Battlefield 3 Premium may possibly come with it I am not sure on that though. Certain dog tags come in certain expansions. So, research one you want and figure out how to get it whether it's buying it or leveling up.
It is impossible to unlock all dog tags in the game, however it is ALMOST impossible to have the dog tags in the TAKEN section, mainly because two of the dog tags you can only get for participating in the creation of the game itself. But excluding those two, it would probably take over half a year, you would have to be playing constantly (I would NOT recommend doing that.) expecally for the gun dog tags and the reaching level Colonel Service Star 100 dog tag.
Battlefield 3 Premium includes everything that the regular edition comes with and some expansions. The expansions are Back to Karkand, Close Quarters, Armored Kill, Aftermath, and End Game. These expansions include weapons, assignments, maps, dog tags, etc.
There are a total of 20 new maps in the 5 Battlefield Premium DLC's. Along with those, there are about 20 new weapons, over 10 new vehicles, 4 new game modes, 30 new assignments, and 20 dog tags.
Battlefield 3's End Game is scheduled to release sometime in march. This new expansion will probably have the following in it: Maps, guns, assignments, dog tags, upgrades, new air and land vehicles, and the addition of motorcycles. End game will be the last expansion for Battlefield 3. After that Battlefield 4 will release sometime in the fall of 2013. Set to release sometime in March.
No, Battlefield 3 does not follow the Bad Company series storyline. Battlefield 3 is a sequel to Battlefield 2.
There is a dog in the campaign. I don't know about any other maps though
Battlefield 3 Premium includes everything that the regular edition comes with and some expansions. The expansions are Back to Karkand, Close Quarters, Armored Kill, Aftermath, and End Game. These expansions include weapons, assignments, maps, dog tags, etc. This was copied from my previous answer to the same answer for a similar question.
battlefield... definately battlefield...