To exchange traveler's checks or foreign currency, your best bet is to head to one of the casas de cambio on Avenida Camacho. Two of the best are Cambios "America," Av. Camacho 1233 near the corner of Ayacucho, and the Casa de Cambio, Av. Camacho 1311 at the corner of Colón. In general, Avenida Camacho is the banking center of La Paz -- you'll find all types of ATMs here, as well as most Bolivian banks. Citibank is nearby at Av. 16 de Julio 1434 (tel. 0800/10-2000); they exchange Citibank traveler's checks for free.
In case of an emergency, call tel. 110 for the regular police. For the tourist police, call tel. 0102/2225-016. For an ambulance, call tel. 118 or tel. 0107/1268-502. If you need medical attention, the two best hospitals in La Paz are Clínica Cemes, Av. 6 De Agosto 2881 (tel. 0102/2430-360), and Clínica del Sur, at Avenida Hernando Siles and the corner of Calle 7 in the Obrajes neighborhood (tel. 0102/2784-001). Farmacia Red Bolivia, 16 de Julio 1473 (tel. 0102/2331-838), is probably the most centrally located 24-hour pharmacy in La Paz. If you need a delivery, try calling Farmacia La Paz at tel. 0102/2371-828.
There is no lack of Internet cafes in La Paz, especially on Avenida 16 de Julio. The average cost is 7Bs (90¢) an hour. You'll find the fastest Internet connections at WeBolivia, Av. 16 de Julio 1764; Punto Entel, Av. 16 de Julio 1473; and Pl@net, Calle Sagárnaga 213 at the corner of Murillo.
The main post office is in a large building on the corner of Avenida Mariscal Santa Cruz and Oruro. The post office is open Monday through Friday from 8:30am to 8:30pm, Saturday from 8:30am to 6pm, and Sunday from 9am to noon.
Punto Entel is the main telephone provider in La Paz. There are two offices on El Prado: one at Mariscal Santa Cruz 1287, the other at Av. 15 de Julio 1473. You can make local, long-distance, and international calls from these offices. It costs about $1 per minute to call the United States -- a bargain compared to what most international companies charge. You can also buy phone cards here or at local kiosks to use the pay phones located throughout the city.