That’s a good idea, but the downside is you have to find and trek to the backpacker hostel. At the airport it’s something to do while you wait for your bags or rental car. Of course, this works in any area of tourist concentration (hotels etc.) but ideally you want it the moment you enter the country. (Indeed, if the current SIM in your phone is prepaid, you may not be able to roam on it at all before you get the new one.)

Cheapest plan may be to order from the best priced prepaid company in advance for delivery to your hotel. Takes advance planning but minimal time. No resale to that, though.

You can cheat with telestial.com. They have often found the cheapest local prepaid company, and they add on thier own surcharge. Use their site to find the company, then order directly.

The site http://www.gsmworld.com is also good for finding the companies.

Also check out my new special forum for sharing this information.