Sign with a provider that supports bring your own device options. This includes Viatalk, Callcentric, VOIP.MS, etc. With VOIP.MS you can actually program the two devices to work on the same DID. With the others, buy a $15 a year account wit Voxalot and program that to connect to your VOIP account. You can now connect multiple devices to Voxalot. They will use the same inbound and outbound connection. If you are worried about congestion issues, back this up with a PAYG outbound account for overflow. Look at VOIP.MS where you can set the outbound calls to spoof your caller-id.

Voip.ms
Call Centric

Opps. Sorry - that's two. I could have named a dozen others too, but didn't want to go too far away from your request of just one...

I have personally done this with both of these providers, so I can confirm that it can be done. eg, with voip.ms I've had it setup to ring my VOIP phone at work, my VOIP phone at home, and a softphone (if it was running) - all with only a single DID.

.....

Just an update, since I've received my 2nd Vonage adapter for the new place . . .

The process of switching lines between adapters isn't as streamlined as I'd hoped. Not only do you have to select the line you wish to move and the port you wish to move it to, you have to enter the E911 information for each line as you move it. And, of course, if you're moving 2 lines, you have to do it twice.

Once you've made the switch, it can take some time before the Vonage devices update themselves and the lines actually become active. I did some testing at my primary residence with both devices plugged into my LAN, and at the moment the reliability of the switchover is suspect (I don't think I've successfully completed a handoff from one device to another without having to power off/on the device I'm switching to in the process).

We'll see how it goes once we set things up in the secondary residence . . .

As others have posted, check out VoIP.ms and Callcentric - two excellent providers that give you a LOT of flexibility (especially compared with Vonage, Skype etc.). What you want is very easy to do; with VoIP.ms, you'd setup a Ring Group for your DID and it would ring both locations. Pay attention to E911 configuration though, that is an important issue.

Personally, I switched from Vonage earlier this year, ported my number to VoIP.ms and haven't looked back. Get a couple of Obi110 ATA adapters from Amazon, sign up with VoIP.ms and save a ton of money vs. Vonage.

Did not see this suggested; to help the OP get better cell service in their 2nd home, they can take advantage of a Femtocell. Basically, it's a mini cell tower that plugs into your broadband connection. The only minus is, one would need to be purchased per cell provider. Links:

http://en.wikipedia.org/wiki/Femtocell
http://www.att.com/shop/wireless/dev...gmicrocell.jsp

or free
 

I got one free from AT&T, just for telling them about how many dropped calls I have at home. I had to pick it up at an AT&T store though, works great.

Another vote for Voip.ms listed above. I do exactly what the OP wanted - I have a couple of Linksys $30 ATA devices and the one phone number rings multiple devices at once and they all share the same voice mail, caller-id, etc, etc. Exactly what you want.

I've been using these guys for a little over two years, very happy, I've heard Callcentric is another decent one.

My monthly bills for all this is well under $5 a month total cost for all my phone usage. My monthly phone bills went down from about $30 a month to under $5, usually more like $3 a month, with a ton of customization available.

I was a little intimidated setting it up at first, but it's actually pretty easy. I also put a SIP client on my iPhone so when someone calls the home number it rings two locations plus my iPhone, so three devices, one phone number, no call-forwarding or anything like that. When traveling internationally I can use the iPhone SIP client to call outbound and the caller-id shows up as my home number and if anyone needs to reach me they can, for no additional cost or international charges.

This is another great benefit of going with a true VOIP solution like VoIP.ms; I've made calls over Gogo inflight wireless, and pretty much anywhere you can get onto Wi-Fi internationally saves you a TON of money.

Lots of flexibility, and you can start doing cool stuff with IVR's (I have a recording for anonymous callers that get dumped directly to voicemail unless they press 1, which gets rid of most robo-dialers for instance), iNum (my wife was able to make a free call from her hotel in Canada to the local iNum access number and get forwarded to our home phone, all free), callbacks, etc.

Amazingly cheap too, I bet most here would end up paying less than $10/month to replace their home landline.

voip.ms has been great
 

I agree with the above posts about voip.ms. I have no other ties to them, BTW.

I am in the process of porting a couple of numbers over and setting up my account. I have nothing but good things to say about their service and help where needed.

It is a bit intimidating because of all the features, but there is great help available and for most people, the defaults are just fine.

You can have incoming numbers from virtually anywhere in the world, and you can turn them on/off whenever you want. Some have a small fee to set up, the rest a very nominal monthly cost (a few bucks I am talking about). If you need a "local presence" in some remote city or country, you can get it here cheap. If you have friends/relatives/clients in remote places they can reach you with a local call. You can have a branch office in London/Paris/Budapest or wherever you want.

About all you need to get started is a less than $50 ATA box (I got my OBI110 from Amazon) and a pre-payment of whatever you want to get started.

The phone lines can then ring to any ATA box, IP phone, smartphone with an ip app, or your cell or landlines. You can forward to international numbers, also.

Rates are miniscule, a few cents a minute to land-lines everyplace, and to mobile/cell phones with their usual surcharges where applicable.

I am so excited about firing the "phone company" after all these years of putting up with their high prices/fees/taxes for an antiquated system.

Well, I've created a voip.ms account and funded it in preparation for receiving my two Obi110 ATA devices. Unfortunately, I realized too late that the Obi110 only supports one telephone line, so I'll be returning them unopened.

Can anyone recommend a reliable ATA device that supports 2 phone lines?

The Linksys (former Sipura) are very good, but by them from a reputable vendor. There are some excellent counterfeits of the unit and those units have had problems.

Didn't realize you needed two lines, are you using a 2-line phone or are you just talking about multiple phone numbers?

I'm using 2-line phones. I have separate business and personal DIDs, and when my wife and I are in the same location we often use both lines concurrently. With Vonage, the business line follows me from home to vacation home (and back), and the personal line follows her. With voip.ms, we're going to simply create a ring group and effectively have both lines assigned to both locations.

The Cisco/Linksys PAP2T seems to be well-regarded . . . any thoughts/concerns?

I have a PAP2T here ... it works great for voice, but does not work well at all f:(r a fax machine. I need a similar device that supports T.38 ...