I'm not familiar specifically with 154.905 or any of the other State of Georgia public safety frequencies but it is my understanding that all VHF frequencies will convert to narrowband, effective 1/1/2013. Hopefully, someone else can confirm that on here. I'm not sure whether that means that all NEW VHF frequencies authorized by the FCC will be narrowband or whether all future and all existing will be converted.
Most folks will aim for 1-1-11 but the mandate is 1-1-13.
Usually a wideband can hear a narrowband (low audio) but the narrowband cannot hear the wideband, it is best not to mix them, once a system switch, they should switch every thing (system and mutual aid frequency's) then training and radio checks by neighboring agency's should be performed.
Unfortunately there will be mobile/portable radios wideband well past the 1-1-13 deadline, causing interference, (itinerant, radios sold at auction, and some that just cannot afford a narrowband capable radio)
Hopefully this takes care of your some your questions: narrowband
I can tell you this. The majority of GA is rural or semi rural and almost all Sheriff's, small police departments, fire, ems are all using VHF analog. There is no way in hell they are going to scrap all their old installed radios to upgrade, most cant afford it.
Go tell 1 of the more than 100 sheriff's that fall into this category to switch to narrow band and they would just laugh and tell you what they have now works great and they dont have the money to buy 1 new radio or repeater much less an entire fleet.
There are actually many county sheriff's offices in GA where the on duty deputy must wake someone up if they need backup...seriously.
I just don't see this happening across the board.
Procopper - I agree with your assessment wholeheartedly!! That is the cold reality of not only radios but most anything else that requires money. Their motto truly is - "if it isn't broken, don't fix it". Interesting - that was very true for so many of the VHF or UHF repeater systems that were replaced in smaller jurisdictions by trunked radio systems. If the goal was interoperability - and so much has been written on here about that - the major obstacles to that are humans and policies, not technical capability.
So, narrowbanding I suspect will be done over many more years than now-2013.