lol... MAXIS really never improve one..

I was a Maxis 3G unlimited user too (after i get my iphone 3G in Aug '08).. and the same thing happened to me.
I chose the Value 50 + 99 unlimited plan, so, after adding the 5% service tax, the 1st month bill came out immediately exceed RM150 credit limit and they barred my phone.

I called to them immediately and scolded the operator "hard hard".. then only they increased my credit limit to RM200...

Anyway, I shifted to Celcom's Executive 20 plan + RM98 unlimited data plan in Dec '08 as it is cheaper to me.. 

@ichuck,
If U don't use, meaning you're going to forgo the entire RM100 p/month for the duration of the contract, it is cheaper for U to buy the phone at a higher price from the 'black market'.

And to answer ur question, U will be charged RM100 + whatsoever Value Added Service u added + 5% GST so ur bill will probably come to about RM100+

@ichuck,
No, if U don't intend to use the line at all then u won't haf to worry about overuse of call charges and SMS charges, etc.  It is things like call forwarding, call waiting, itemised billing, etc.  Just cancel those and I think your bill should be RM100+5% GST.