If it were an honest mistake on their part, I 
would probably ship it EMS.  Unfortunately in 
their emails before the end of auction they said 
they didn't like the price of EMS but still 
wanted it.  They even asked me to charge them 
less for the EMS.  So this was no honest mistake 
but intentional.  I've already emailed them back 
saying that they didn't pay the correct amount 
and as it stands the cel would be mailed 
airmail.  

I had a bad feeling about them from their emails 
before the end of the auction and should've saved 
their userid to block them from bidding.