Call Failed on iOS 4.0.1 Iphone 3GS JB

Hi,
I use these setting too. MMS/Browsing/3G no problem. Sending sms & also receiving call. But on top of that, I can't make a call!!
Recently switch to Celcom from Maxis.
Device:iPhone 3G S
OS :iOS4.0.1
JB :Ultrasnow 0.93
Unlock : Yes

I have tried every threads,heaps of links & couldn't solve it. Sometimes when i enable TTY it's fine & making call is easy but sometimes i cannot make call absolutely whatsoever.
Upgraded iTunes recently to 10.1 using windows xp SP3.

Can anyone here could be a dear and please help me?
I was a WinMo fag switch to iOS cos WM7 is too late & only a preliminary specs.
Currently developing on X-DA

TQ