The T2006 set was released between 1909 and 1911 by the American Tobacco Trust. The 'complete' checklist for the set is typicaly considered to be around 520 cards. The cards were not numbered, and there are multiple different backs for each card, making the full number of 'different' cards well in the thousands. The biggest card from this set - possibly the most famouns baseball card ever - is the T206 Honus Wagner, which was reportedly pulled from distribution after Wagner objected to being used to promote the use of tabacco. This one of what are referred to as "The Big Four" - four cards which are considered the hardest to find and the most expensive in the set: Honus Wagner, Sherry Magie (incorrectly spelled, common version is correct at 'Magee'), Ed Plank, and Joe Doyle ('NY-Nat'l', common version just has 'NY'). The set features 389 major leaguers and 134 minor leagues, with some players having multiple poses and/or appearing with multiple teams. In addition, some cards have printing variations which resulted in parts of the card not appearing; these variations are not always noted in checklists for the set.
For an excellent web site on this set, take a look at www.t206.org
The images below are scans from a reprint set I have. Oddly enough, my reprint set includes a second card of Eddie Collins that does not appear in the checklists I have found for this set. Who knows what that means.
T206 White Border (T206) 1909-1911 (Set size 525)