you see there's the mis-conception...
Phone service in general (any network) can and does vary by handset. Oh and by the way....I am fortunate enough not to live in the US.
so to answer your question directly...
Amongst other things, the blackberry takes and makes calls far better than an iPhone can. It holds onto to its' signal better and the quality is far crispy.
you realise you miss a proper phone the first time you drive to an area with an iPhone where with your old phone you got a signal (not a good signal) but on the iPhone its nada, zilch...
same sim card..
so you go home check the network map ....yes you should get coverage...so you ring the network...any issues in that area? No.... so how come I had to drive 3 miles away to get any sort of signal??
Are you on an iPhone sir?
Yes...
Ah, that explains it...
or
at the office in a major city where its 5 bars 3G on every network and the phone is on your desk not touched and suddenly you get a text saying 'missed call..this person tried to call you at...'
the phone never rang, its a foot away!!!
or
again in a major city in a life or death situation where you really need to ring a loved one and the phone screen stares back at you with 'searching' in the top corner....to the point where I have to borrow a friends phone on the same network just to make a call.
iphone still says searching....
you know just basic functions, most any other phone handles better.
Apple are happy that you blame the networks...but the truth is, it isn't the networks fault. iPhone is just a really poor telephone handset.
Can I play Madden NFL on a berry? Probably not, but then again I didn't really buy it for that did I?
just on a serious point I've managed to test iPhones on all 3 of the major UK networks and you can name any other 3G phone by any manufacturer and they will all perform better.
I've got companies begging me to find them something that actually works and to get away from iPhony's