O2 have the worst coverage of all the providers where I live. I live in a rural area in the SW of UK. With voda I can get 3.5g upstairs, orange 3g, 3 3g, and o2 not even edge !! In my last house I often could not get a signal on o2 hence I changed networks.
So it is important for me to be able to unlock the iphone just to be able to use it !!!
In your house you should probably have wifi, it's better than all the above put together. The iPhone is great at picking up wifi (better than my Macbook and MBP).
However, I could be more impressed by O2s coverage. I know it was not so great for 3G but I was hoping O2 had sorted EDGE out. It's a software upgrade to the GPRS infrastructure after all.
My experience does not reflect the service announcements in the above link posted.