I got quite a shock with my latest O2 bill - it has more than doubled.
Since last October when I switched from Vodafone to O2 when I got an iPhone my bills have averaged between €50 and €60. I am on the lowest tariff available for the iPhone - "iPhone 175". This allows 175 minutes talk and 100 texts per month. On my most recent bill I had used only 53 minutes and 36 text messages. On examing my bill I could see that I had been charged almost €60 for "Roaming" - this of course was as a result of my trip to Reading in the UK last weekend, which was my first trip outside of Ireland using the iPhone. Most of this was made up of Data Usage - I had only a few calls and text messages.
On the bill I note that my total Data Usage spend was €44.81 (+ VAT). My total for four calls for 4 mins and 47 secs was €3.46 (+ VAT). Two separate data costs were just over €12 each - I reckon these were due to using Google Maps to find my way around Reading. Each was for about 1.45MB of data. Total Data Usage was about 5.5 MB - about the exact same file size as the song Bohemian Rhapsody (5.58 MB). Apart from Google Maps I looked up train and bus time tables.
As I was passing through Dublin Airport on the way to Heathrow, they were selling small hand-held SatNav devices for only €99, but I said to myself "No point in buying that, sure I have GPS and Google Maps on my iPhone"!