Colombia also has Comcel (
www.comcel.com.co) which is GSM 850. Keep in mind that in any major city any of the three companies should be ok. Please note that the last time I was there Comcel wouldnt hook up a prepaid account without a cedula. Tigo would accept my passport and movistar was still Bellsouth last time I was there. If i had to guess I would probably say you were better off with Tigo or movistar.