Can a prepaid quad-band international phone be used to read email in foreign countries?
Not directly, but 2G data access can be made to work, easily (not just 2G data, but also prepaid international talk/text if you opt for option1, below). [This is a result of the universality of GSM technology (AT&T and T-Mobile) when compared to the limited applicability of CDMA technology (Verizon and Sprint).]
OPTION 1: VIA CELLULAR DATA (EDGE). If your phone is unlocked, and you want cellular data (2G) get a prepaid temporary foreign SIM. This is best bought on a local shop abroad, if you know the language, and will enable talk/text/data at the lowest cost. Buying the SIM in the US, before your travel, is possible but not cheap relative to the local option, and may not have a GPRS/EDGE option (for data). Example: www.telestial.com
OPTION 2: VIA WIFI. If your phone is WiFi enabled, go to a local Starbucks, data is free and you are good-to-go. Free is good *grin*
Depending on brand/model of phone, unlocking can be done simply by code using a reputable eBay listing. One example I have used three times before: http://stores.ebay.com/UnlockG