turns off during calls

[GK2011]

Hi,

I have a JBn unlocked Iphone 3GS 4.2.1

During a phone call lasting 6 mins the iphone shuts down and all I am shown is the logo!

I use greenpoison and it reboots but then during the next call of 10mins it crashes again.

Has anyone a solution please as to get over this issue

I have tried rensn0w untethered and greenpoisi0n tetheered to get it up and running again!

Obvioisly i want it not to crash during a call

Many thanks in advance

GK

[z3r01]

Restore and re ail re-jailbreak

[GK2011]

tried re jailbraken about 5 times now still no luck?