After much hiccups with losing MMS, 3G, Voicemail service on IOS 4.0, the struggle to change it back to 3.1.3 is strong. I spent hours reading and testing and I have successfully downgraded from ios 4.0 back to 3.1.3 using DFU mode restore in a VMWARE Workstation. To kick off the recovery loop, the tool “recboot 1.0.2”

Note : /etc/host file need to be modified to point to with the ip address.

here is a picture of the successful downgrade, base band remains as ios4 but firmware is 3.1.3 running on MobileOne (M1) Singapore.

Any queries please post here.