If you were waiting for a bargain basement iPhone you'll have to wait a bit longer. The Voda iPhone kicks off at £30 a month - £5 cheaper than O2 but the same as Orange. If you want it free than it is £35 on a 24 month tariff or £40 on an 18 month contract. If it is a free iPhone 3Gs then expect to pay £45 a month.
Other things worth noting
£70 per month (on 24-month) will get you a free 32GB and 3000 minutes of talktime
The phone comes with 1 GB of data - which is slightly more than rival networks are offering
Unless you are on the cheapest deal you get free unlimited texts
Customers also get free Vodafone to Vodafone calls
More details here