I keep track in only very general way.  I use 
Quicken for all my accounting (both business and 
personal). I keep detailed records for everything 
I buy except "entertainment" items such as cels. 
They are all pooled together under the same 
heading (along with movies, video rentals, books, 
CDs etc). I can tell how much I spent on cels in 
any month but I couldn't tell you which amount 
went for which cel. If it was a light purchase 
month I could probably narrow it down and figure 
it out, but if it was a heavy purchase month I 
would only be guessing. It wouldn't be too 
difficult to keep track by simply adding that to 
the record as I make the payment, but it seems 
more of a hassle than it is worth. I really only 
need to keep track of the monthly total to keep 
within my budget. Once I have bought a cel I do 
not intend to sell it, so why put in the extra 
time and effort?