Please read this. Its not from me, i have found it with google.You have only one service bar but it works.

I had the same problem as many of you. I have an iPhone 4 on preserved baseband 01.59.00. I used sn0wbreeze 2.9.10 / 2.9.11 to jailbreak 6.1.2 and preserve baseband. Immediately after jailbreak success, I found out that my signal is cycling between "searching / 1 bar / no service" every minute which essentially makes the phone useless for calling or 3G data. The no service cycling error does not seem to have anything to do with ultrasn0w since at this point I have not even installed it. I tried with activation / no activation / baseband preseve only + evasi0n separately without any success. I must have tried for hours, with many different combinations.

Installing ultrasn0w 1.2.8 will cause my phone to have no service all the time so I think 1.2.8 + iphone 4 + 01.59.00 + 1.2 has some issue.

However I did manage to get the cycle between "searching / 1 bar / no service" every minute to stop and now I'm left with 1 bar (all the time) without installing ultrasn0w. For those whose phone is locked to another carrier you probably need to wait for new ultrasn0w but the procedure I have below worked for me. edit: I only tried on a fresh install of 6.1.2 with sn0wbreeze, i4 01.59.00.

1) Get the latest version of redsn0w - 0.9.15b3. 2) Get the iphone 4 6.0 firmware iPhone3,1_6.0_10A403_Restore.ipsw (this is the latest supported by redsn0w for now) 3) Go into redsn0w, go to 'extras' select "select IPSW" and pick the 6.0 firmware 4) Go back to main menu, select jailbreak and perform a tethered jailbreak. 5) After its done, the phone should still be untethered but I find that the cycling is gone.

This should hopefully get your phone somewhat usable until there is a ultrasn0w fix for the 6.1.2 / 01.59.00 combination.

I don't really know why it works but I got desperate so it was worth a shot for you. I've used it for the past 2 hours and the phone no longer goes into "no service"

edit: Seems like if I restore from backup the problem occurs again. I'm not able to pinpoint what the portion of the restore is breaking it (settings, apps, etc.). Last night after I thought it worked (2 hours)I tried to restore all my old settings and apps and then the signal problem came back. If I run the jailbreak procedure above after I restore it will fail and the phone goes into restore loop. If I begin all over again then it'll work again - its just that I can't restore from backup.
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junlaylo