Once a GSM (SIM-based) phone is unlocked, then used, does it need to be unlocked again?

Once a GSM (SIM-based) phone is unlocked, then used, does it need to be unlocked again?

joe.attaboy asked:
I own a Palm Treo 650 that I’m about to replace with a Blackberry, and I’d like to sell the Treo on ebay. I bought it new from a dealer (not from my cell provider), and it was unlocked for GSM systems (T-Mobile, Cingular, etc). I’ve used it for over a year now.

Will an T-Mobile Sidekick 2 phone work with Malaysia’s U-Mobile 3G 2100 service? I really want a Sidekick.

Will an T-Mobile Sidekick 2 phone work with Malaysia’s U-Mobile 3G 2100 service? I really want a Sidekick.

royaltylites asked:
here are links to the phone i intend to get (if it works here):
http://cgi.ebay.com/SIDEKICK-LX-BLUE-TMOBILE-SEALED-NEW-IN-BOX-UNLOCKED_W0QQitemZ250263304240QQihZ015QQcategoryZ3312QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
and
http://cgi.ebay.com/Sidekick-2-II-T-Mobile-Unlocked-GSM-QWERTY-Cell-Phone_W0QQitemZ170233234121QQihZ007QQcategoryZ3312QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
sony erricson slide phones

how can i register an unlocked phone?

how can i register an unlocked phone?

awsomeperson asked:
I bought a phone that was “unlocked” off the internet. How do I register that phone with t-mobile, or any other GSM network user? By the way, its this phone.
http://etronicsland.com/m800-gsm-triband-unlocked-cell-phone-mp4-wristphone-watch-p-218.html?currency=USD
Cell Phone Magazine

What exactly is an “unlocked” phone?

What exactly is an “unlocked” phone?

JJ asked:
I bought an “unlocked” phone off of eBay and I really don’t get what I am supposed to do. Is there a special SIM card that I need to buy for the carrier that I want to go with? Its a GSM phone and it can be compatible with these carriers: Fido,

GSM mobile phone tracking?

GSM mobile phone tracking?

Jay asked:
is it possible to locate a mobile phone just by the SIM number (mobile phone number) but without using the IMEI number?
CellPhone News