I am looking for a reasonably priced used GSM 900 Mhz cell phone in US that I could use overseas.

Just get a 900MHz and 1800MHz dual-mode phone, it would be far less hassle, there is little price difference and you'll be covered to roam just about anywhere in the world bar Japan. Tri-band phones are increasingly common so you could probably bolt on the US 1900MHz/new 850MHz standard.

Several things:1) When you buy a phone in the US, there's a really good chance that it will be locked. Which means that you won't be able to go to EU and just but a SIM card and pop it in. When buying a phone, look for an unlocked phone! You can also unlock it yourself by paying someone to do it for you but that takes time, money and most of these people are shady.2) Buy a Nokia Worldphone. It has support for all frequencies. Nokia 6610 is a nice one.3) Buy a phone on eBay (make sure it's unlocked!) and buy service from T-mobile or Verizon. When in EU (I presume that's where you'll use it?) buy SIM cards.