Vodafone Pay Monthy Contract?

[Claire]

I have had my Samsung Tocco Ultra and i have had my contract with Vodafone for a year now. I set up the contract with Phones 4 U. The sales assistant told me that if i was going to stay with Vodafone at 18months i would be able to change my phone otherwise i have to stay for the full 24months. But from logging in to my account on line I find that i can’t change my phone till 17th July 2010. Now i seem to think i should have come direct to the Vodafone shop rather than go to Phones 4 U and been told false information. But after this i am wondering if i am able to upgrade my phone at this time to the Iphone 3G, i have had a look around the Vodafone website to see if i could find any information about this such as would i have to pay a lump sum to able me to upgrade my phone and i am looking to stay with Vodafone as i have never had any problems with you. As anyone tried this or could tell me what might happen thanks for reading