Let me make more suggestion, if you use the por llamada option for calls back to the US at $1 a piece, its 30min or any fraction of that for $1. So, what I do is use this is conjunction with a calling card. This allows me to essentially make multiple calls with my calling card so I dont pay $1 for a voicemail pickup or a very short conversation. Very well worth it. Take a look at
www.uniontelecard.com for cards, I use them all the time and they have excellent prices including clean cards and you can just hit "###" on the phone to end the current call and get a prompt to enter the next number you want to dial. If you have any more questions I would be happy to help.