If your phone has a blacklisted ESN it is a paperweight. The only people that can unblacklist an ESN is the carrier who blacklisted it. Jailbreaking or restoring will not make you able to use a blacklisted phone.
I have an american clear ens iphone3gs that works perfectly in italy after jailbreak when it shouldn't. so the problem is to clear to esn.
1) on he internet i found that a bad esn phone (eg. blocked by verizon) can be used with carriers rather than verizon. is it true?
2) some say you have to "flash the phone" in order to use it with another carrier. do you have any idea how to do it??
3) I heard that a bad ens iphone works perfectly but cannot call. so is it true that the carrier block the phone when so that it cannot connect to the net?
When a phone has been blacklisted only the carrier who blacklisted it can unblacklist it. You could try and use a different carrier but it would still be blacklisted.
CDMA iPhones cannot be unlocked, only GSM iPhones.