Hello Everyone,
This is my 1st post. I also have a bell iphone 5 that is connecting to 3g only. I have done all your suggestions ie network reset, remove sim, device restore etc... and 4g LTE does come on for about 10 to 15 seconds and still switches back to 3g. (Yes, I do live in a 4g LTE area)
Here is some info I have found...Bell, Rogers, Telus are all having issues with iphone 5 4g LTE connectivety. However a lucky few iphone 5 customers are not having any issues with 4g LTE.
Now, Android 4g LTE devices on the Bell network (can't verify rogers or telus) in my area (actually right beside me in my house) has no issues with 4g LTE connectivety, it is at full strength.
I have read many posts as I am sure most of you have that Bell Rogers etc are not the only carriers with this issue, carriers in the United States are having the same issues.
My conclusion is that its not a 4g LTE network problem or a carrier misleading its customers for 4g LTE coverage, it has to be a iphone 5 problem, not sure if iOS 6 reverts back to 3g if it thinks the signal is stronger or something is missing in the iOS 6 4g LTE protocol.
I am hoping there will be an update to iOS 6 to fix it soon and I am praying its not a faultiy hardware issue, fingers crossed.
Cheers
James