I'm kind of in the same boat.
I bought a phone off craigslist didn't work now im stuck with a phone i can use wireless on. attempting to make a call, the call drops instantly , received calls go straight to voicemail.
after researching all this past week.. i've noticed the following probles so here is my situation at hand.
i have the IMEI issue with corrupted characters except mine says 04 at the end.
unable to root.
unable to put this phone in download mode
(attempting to fix the imei issue reflashing with odin)
I have no back up files
unable to enter recovery mode manually. I read from another thread someone was able to do so using t mobile one click root program for vibrant ,
which works for this, but when i tried to root i get e signature verification fail issue as well.
I've read countless threads and forums and about to inquire to samsung or t-mobile for a repair. my aim is to get this phone operable.
i'd like to help myself on the issues but find myself at a dead end with being unable to put in download mode ,and yes ive tried the different methods of holding buttons/ inserting usb.
and at another dead end being unable to get this rooted because of signature verification fails.. any help or direction would be greatly appreciated.