Using your phone as a modem

Hello,
I Have a Sony Ericsson C905 and want to enable it to use it as a modem for our laptops for free, How do i do it for free.

My Brother also have a Samsung Pixon M8800 and know someone who does and are desperate to be able to use our phones as a modem for our laptops but when my provider has offered me to pay an extra montly fee to enable my phone to be used as a modem, But we told him a straight no, How do you enable it for free.

My Dad has a Nokia 6300 and would like to be able to use it as a modem for free on his laptop, How do you do it for free.

My Mum has a Nokia 6500 and 6600 and would like to be able to use her phone as a modem for her laptop, how do you enable these phones to do this for free.

Thankyou