Hi there Mish!
I got a VOIP line at
www.terrasip.com and pay 35 dollars every 6 months for a Buenos Aires land line incoming number, plus only 1 cent per minute to almost every destination in the world.
If you buy a PAP2 addapter at
www.mercadolibre.com , you can connect a regular wireless phone. The service is good and cheap. The catch: you need an internet connection.
I don't know telecentro, but they give you cable, high speed internet and a phone line for something in the range of 130 pesos per month, which is a great deal!
Take care.