There is only 1 reason to switch to VoIP... to Save Money!
You can save tons of money using VoIP rather than PSTN phones.
If you already have a cell as your backup comms and 911, then I say go for it...... get VoIP!
Yes, there are reliability issues related to using VoIP.
Yes, if Internet goes down, so does your VoIP phone, too.
These days, Internet connections are highly reliable.... at least where I live in Alberta, Canada. Over past 4 years I have had DSL Internet, and now Cable Internet..... both have been Very Reliable with no down-time, that I can recall, in past couple years.
"Most" reliability issues people have with VoIP is Not with service providers, but with your Equipment Hardware, such as Modems, Routers and ATA VoIP telephone adapters. Most VoIP services sell you VoIP hardware made from the same big-name manufactures (perhaps re-branded for their service name), such as Linksys, Motorola, Grandstream, etc. The equipment is reliable, BUT problems usually arise due to "configuration" problems that don't work for a particular situation or circumstance. It helps to have a little tech-savvy when problems arise....
Problems can be compounded when your equipment is Wireless-G. So, it comes down to how tolerant you are about dealing with technical issues when things go awry or need a little "tweaking".
I am currently using VoIP 100% for all my phone calling.
I officially pulled the plugh on Ma Bell six months ago and hope to never go back. The savings are substantial. I get a lot more features and flexibility at a much lower price.... how can one ask for more?
I use InPhonex as my "primary" home-phone VoIP service provider. They provide E911 where I live in Canada, even though InPhonex is a USA-based company. (find link through my profile)
I have their "LiteLine" service for $7.95/month.
I use CallCentric as my "secondary" home-phone VoIP service. I have a local-area phone number for $1.95/month + 1.5 cent/min incoming and 1.9 cent/min outgoing calling + all bells & whistles for free that Ma Bell charges an arm&leg for.
CallCentric is BYOD (bring your own ATA adapter).
So, I purchased my own Linksys PAP2T phone adapter through VoIP Depot in Canada. I configured the PAP2T for InPhonex on the adapter Line-1, and configured it for CallCentric on Line-2. So, I have just 1 VoIP adapter configured to work with 2-separate VoIP service providers.
CallCentric and InPhonex provide free softphones so you can use their services with a PC too. Or, use a 3rd party configurable softphone with their service, such as CounterPaths's "X-Lite" free downloadable softphone.
For alternative softphones and PC calling I also use Gizmo Project (now Gizmo5), Skype, Efonica, and Hotfoon.
So, even if you don't pull the plug on AT&T completely, you can use VoIP to save tons of money on long-distance calling alternative.