Call AT&T and tell them you want a "Remote Forwarding Number". That is what I have had on my primary business line since 1998. It is a number in cyberspace that I can point to whatever number I want to...cell phone, land line, Google Voice, call service...whatever. Rather than porting ever time we move or switch services, I just set up the service I want and forward my business line there so I own and control my number at all times. It is not tied to a twister pair or physical location.
Oder that so you can get your number than port from there.
That works but if you need the outbound caller ID to match when you dial out, you have to resort to some VOIP trickery. Or if the outbound calls are on a business T1 and you're set up correctly to send it, you can sign some paperwork asserting that you own the other number and the carrier can unblock the filter at the CO that keeps you from announcing / spoofing Caller ID outbound.
Most people call folks back these days from whatever they got on their caller ID. They don't bother even listening to any voice mails that got left.
How you handle outbound caller ID is a pretty significant engineering step when installing a business phone system these days.
We announce direct numbers for managers and people with direct to the public job roles, and an 800 number for any phone or softphone associated with any agent licenses in the callcenter.
The 800 number comes back to a custom IVR menu just for those portions of that business and bypasses the main IVR menu that handles all five companies that take phone calls on our system. It also locks the return caller out of escaping to the "Operator" queue and offers no way to get to "dial by name" or "dial by extension", they must pick a queue over in that department that'll take them back to a call center agent.
Only certain agents may accept inbound calls from that "unknown" queue. They have special training on figuring out who is calling back for whom and have rights to transfer into other queues.
Conference room phones also get their own outbound direct caller ID but they're set to never go to the menus and never go to voice mail. They'll ring inbound and that's it. If no one is in there, you called for your conference at the wrong time, or you need to go look at the emails from people you're working with and call their real phone numbers.
Three phones are associated with one of the sub-businesses. Those have CID direct back to them on one line and a CID meant for outbound calls that might come back to anyone in that team, that goes to a menu for them, on line 2.
The only two phone lines in the entire building that we don't have to send oddball caller ID outbound for, are the fire alarm analog lines. And they never touch the PBX. (In Denver we're allowed to use one analog line dedicated to the fire panel and back it up with one analog PBX line by law. We decided it wasn't smart and just pay for two. We could also install a cellular backup. Cost wasn't any better and we kinda like the idea that the FD is really coming if the panel alerts.)
I geeked out last October designing this thing. It was fun. The only tricky part was the phones that live on people's home office desks in other States. They had to be labeled "Caution: Dialing 911 on this phone will call DENVER police not LOCAL police."
We also set up an email alert to all the admins and managers if someone does dial 911. It happens about weekly. We coach and coach but people still panic and hang up, triggering a call back and a dispatch if we don't answer. Because, callcenter. I jammed a two second delay in the emergency dial out script before actually placing the call, figuring nobody is going to die in two more seconds. It dropped the number of actual dial outs to 911 by over 90%. At least people are quick when they panic and hang up. Haha.
Last time one really went out, DPD officer stood over in Marketing flirting with one of the married ladies for an hour. She liked it and was flattered for about five minutes and then literally turned her back on him and went back to work while he kept talking for 55 more minutes.
The whole thing was line of sight from my old desk so at about the 20 minute mark I went over and attempted small talk to remove his targeting system from my co-worker but it didn't work. As soon as I had someone walk up needing something IT-ish, he started talking to her back again.
He was left handed and carried a Glock 22, I noticed. What a slab sided beast that chunk of plastic is. He was one of those who likes to hook both thumbs behind his holsters. Taser was on the other side.
Standing there talking to her back at her desk he came across as "douchy" at best. Hahah. I almost asked him if he was lonely but I couldn't think of how to make it enough of a joke to keep him wondering. Almost raised the delay to five seconds that day, too. Hahaha.
