There are three wireless carriers in Bolivia:
This is a privately held company, which however has a stakeholder which is a local communications cooperative in Cochabamba (COMTECO). This carrier uses GSM and provides GPRS/EDGE access. In general this carriers works with the 1800/1900mhz.
This is a privately held company, which provides GSM with EDGE/3G services and also Blackberry services.
This carrier works with 850/900mhz
This is the recently nationalized carrier in Bolivia, previously owned by TIM. It provides GSM with GPRS/EGE and also Blackberry services. It also still has a legacy TDMA network which is still supported. This carrier works with 900/1800/1900 mhz.
If you visit the websites of any of these carriers you will find an option which lets you send free SMS to any mobile phone in he country.