actually the 8890 is a gsm world phone, as long as your phone takes a gsm sim card it should work. I have noticed that my ericcson t68i does get a little bit better reception. The unlocked refers to the fact that you can put any providers chip in it. Most cellphones that you get from a provider are "locked." This is so that you must use the phone with the provider that you bought it from. An AT&T t68i will not work with a cingular sim card and vice versa. The big advantage of having an unlocked phone is if you travel to other countries that use GSM primarily, you can buy a prepaid sim from a local provider and use their service at their rates instead of the "world" rates that cingular charges. The last time my brother went to Taiwan cingular's world rate was about $6 a minute, so it was much cheaper to buy a local prepaid sim and use that instead.
BTW, I am currently using an erricson t68i and have been very happy with it. Battery life is much better than the nokia's, the ring is loud, and it has bluetooth so you can use wireless handsfree headsets as well as data transfer. I believe they are available from cingular as well, but if you are planning to go abroad I would try to find an unlocked "world phone" that covers all bands, not just the ones used in the states.