Ther are plenty of breeds small enogh to be carried round...
However anyone purposly breeding dogs small enough as adults to be carried in a pocket is NOT a good breeder. Terms like tecup, tiny toy, pocket ect are buzz words used by petstores mills and back yard breeders to advertise and get more money for their undersized, usually sickly litter runts.
The smallest breed is the chihuahua...
Breed standar calls for a dog between 3 and 6 lbs... 3 lbs is TINY and anyon breeding for smaller isn't. Worth he trouble, bred smaller they tend to be prone to many health problems
at 3lbs my smallest likes to be carried... But he also walks perfectly on leash!