which Iphone 4 plan should i buy?(australia) read info.?

[caglar]

I am thinking of getting an iphone 4 16gb phone. I don't know wihch plan i should get. I work and get paid about 250 a month. i want a plan which will be suitable and it will have unlimited facebook,calling,text, etc. there is this one : look at this link from vodafone:http://shop.vodafone.com.au/mobile-details/apple-iphone-4-16gb copy that and yeah. i dont know why it says plan: $45 a month and then on the right of it, it says, mobile: $18 a month. i don't know if i should get that, tell me what is good about that , and if i will beable to afford that. do i have to pay for the full phone like, $850 lets say for the phone, then the plan? or is it , i get the phone and then pay for the plan, and also there is this : http://personal.optus.com.au/web/ocaportal.portal?_nfpb=true&_pageLabel=Template_woRHS&FP=/personal/mobile/mobilephones/handset_details&site=personal&mt=handset_details&sort=d3e72a394f6196ccf6addc933bea2cdd213041e9f|24 thats optus, i dont know which plan to get, so yeah, please help me!