Either way is OK, can buy with new number or use existing number, so long as you don't have an existing contract

Yes, you have to change your existing monthly commitment to either one of the five options available: - maxis One Plan, iValue 1, 2, 3 or 4. The plan you choose will then become your new monthly commitment.

For now, mostly you can only find 16GB variants of the phone, and yes, it varies from center to center.

Reimbursement period for advance payment is over 5 months, if not mistaken. If you have been with maxis for more than a year, they can waive the advance payment.

Assuming you haven't been with maxis for a year and you want iPhone 6 Plus 16GB on iValue 1 for a 12 months contract: -

When register, pay 2,199 (device price) + 300 (advance payment) = 2,499

1st month to 5th month: Bill will be 100 - 60 = 40 monthly (60 x 5 = 300)
6th month to 12th month: Bill will be 100 monthly

Hope that helps.

i got mine with 12-month installment using HSBC card with 0% interest and Rm0.00 processing fee from Maxis centre

but i think different maxis dealer have different machine from different banks, try to ask around.

even switch and machines accept installment from cc!

Try sengheng / senq
Not sure about stock availability though.