They also offer an NA-style plan where you get the Android flagship handset for free when signing up for a 2-year £30/month plan.
Leaving aside the invoice price Carphone pays, these 2 options to get the first Gingerbread phone tell an interesting tale:
the handset component of the monthly payment is 430/(30*24) or 60% while network (data+voice) use - the remaining 40%.
It would be a real stretch to extrapolate those numbers to other handsets/plans/countries but claiming that only about half of the monthly payment in any plan offered in NA with a "free" smartphone handset goes towards network use (and the other half is the price of the "free" phone) would probably be a safe bet.