Hi, I'm looking to get a Treo 600 but am a little confused about some of the stuff I read here about the "unlocked" version. If anyone can throw some light on this, I'd be eternally grateful

1. I'm looking to use either T-Mobile or Cingular. Are these guys ok with me signing up using an unlocked Treo?

2. I've read that some software upgrades "lock" the phone so that it's no longer unlocked, thus undoing the benefits of being unlocked. True?

3. If #2 is true, how do I avoid this?

4. Anything else I should know? Are some services/features unavailable on the unlocked versions? I'm looking at T-Mobile mostly -- has anyone used the unlocked Treo with these guys?

Thanks to all who can throw some light on this!