Can my BES synchronize my Exchange with two GSM card from two different network.

The issue is this. My company have about 20 exteremely mobile staff operating on two different country. (Singapore & Indonesia) and they are all addicted to their blackberries. In order to deal with the roaming charges, I plan to equip each of them with two GSM SIM (from SingTel (Singapore) and Matrix (Indonesia)) but I want to configure it to both synchronize to the same Exchange account. So they can just plug in the card appropriate for the country they are in. Will this work?

Do I need 2 BES user license per person then?