Although Verizon hasn't announce a release date for the phone, they have been advertising it heavily (albeit as "coming soon"). They also did say 1Q11 (which, in theory, could be 3/31/2011). So... let's say for sake of argument they had planned to release the phone by now, but haven't due to "issues" - it comes down to a business decision to delay it further:
Delay due to:
1. Poor iPhone Sales - we have to wait until they hit a specific number. Likelihood = 10%. I can't buy this - two different customer bases.
2. Features "Promised/Advertised" Not Working - they have to get them working before release. Likelihood = 50%. I think if it was just one feature (e.g., Skype Video) then they would pull the trigger and release it and update it later, but if it is multiple features... then they probably hold off.
3. Battery Life with 4G/LTE - they have to get it to "point X" with normal use (e.g., 6 hours of Angry Birds play
). Likelihood = 75%. I think this would be bad PR for the device - since it is something that is harder to fix with a firmware/software fix than a feature issue is. If it got to the point that they needed to pop a new battery in there.... wow... that would be huge for them.
4. Technology issue with 4G/LTE - there are issues with it working with the new network and since this is the first 4G/LTE phone... they want it to be as close to perfect as possible. Likelihood = 10%. Would think that this would have been discovered before this point.
My guess is that there is an issue with the battery and there is some furious discussing going on as to what to do. It's not like it is a sw bug and there is a line of code you can remove to get it to work right.
MAYBE the whole $249/$299 issue is related to them needing to put in a bigger/better battery and needing to make up the cost of it.