Then real life.  The main reason why you sold the 
cel was because you needed the money as soon as 
possible.  The buyer agreed to this and it seems 
to me that he is the one that has breatched the 
contract.  I would offer him one final day, a 
mark of payment.  Like your car payment, if you 
don't pay at a certain time you get your ride 
repossessed by the bank.  Give him a final date 
of when the payment needs to be recieved and if 
it is not recieved by then put the cel up on ebay 
with a buy it now price the amount that is still 
owed on the cel.