How Do I Filter Phone Calls on a Land Line?

An anonymous reader asks: "I have a telephone on a plain old land-line, with the option of subscribing to caller-id. I would like to filter incoming phone calls, diverting them to either the handset or answering machine, based on whether the caller-id matches a list of trusted phone numbers. Considering that many of today's land-line telephone handsets can display caller-id and store a list of favourite phone numbers, I don't think this is technologically difficult. AI am not interested in: subscribing to a service provided by my telephone company. I would prefer the filtering occurred on my side of the phone line, or implementing a software solution on my PC. Frankly, that is overkill, and I don't want my PC turned on permanently. I would prefer something like a small, solid-state hardware device. Is there any such thing available?"

Comments

The same way everyone else does

[0racle]

An answering machine. Don't answer till you know who it is, and if they don't leave a message you probably didn't want to talk to them anyway.

Re:The same way everyone else does

[Alien Being]

Not quite right. I think the real question is which answering machine has the ability to ring or not-ring based on caller-id info. I wish my own answerer could do that. It should have these options to control whether the phone rings:

Ring/don't ring for blacklisted callers
Ring/don't ring for whitelisted callers
Ring/don't ring for new but identified callers
Ring/don't ring for unidentified callers

It should have similar modes controlling whether or not the machine will accept a voice message. That should all be simple to implement in a device that connects like a regular phone (in parallel). When reviewing the incoming calls, it should be a one-touch operation to specify how the machine should handle future calls of the same type.

The super-duper version should have the ability to sit between the phone line and other devices (series) and use a speech synthesizer and recognizer (or dtmf decoder) to allow control from regular phones throughout the house. e.g. A call comes in, the phones give a single short ring as the machine announces itself to the caller. If a person picks up a phone, the machine tells him whatever it knows about the call and asks whether to hangup, connect, or take a message.

Re:The same way everyone else does

[LordNightwalker]

"Hi, it's Mike. I'm not in, so leave your message after the beep" costs you less 5 seconds of your life. If the answering machine is set to pick up immediately, it will even *save* you time, because the machine will have picked up before I have the time to walk over to the phone and pick it up manually.

On the other hand, you might be that pesky asshole I don't really want to talk to. You know, the one that won't shut up, the one I can't possibly end a phonecall with in less than 20 minutes without being rude.

So let's do the math again:

• You call me, leave a message after the beep. You lose: 30 seconds total, 45 tops.
• You call, I pick up, you're the talkative asshole. I lose: at least 5 minutes, possibly half an hour or more.

My time doesn't have to be more important than yours to justify my screening of the calls; I stand to lose more time than you by picking up the phone. You can whine about it all you want, that won't change the facts.

Besides, my time might very well be more important than yours, and probably is. Remember that you're the one picking the time of the call, not me. You time the call to coincide with a moment you're not doing anything important anyway, unless it's an emergency call. Chances are I'm actually in the middle of something. Are you trying to tell me that whatever it is you want to tell me is more important than anything I might be doing at that time?

If whatever you want to tell me is important enough to interrupt my shedule for, it's important enough to leave a message for. If you can't be bothered to interface with a machine for 20 seconds to help me manage my time, I can't be bothered to interrupt my shedule to talk to you.

Handset.

[jfisherwa]

The cheap Uniden dual-handset receiver that came free with my SunRocket service has a built-in phonebook, complete with user groups and different ring-tones. Set the default ring-tone to nothing/one quiet beep and put everyone you know into groups with a real ring.

No PBX, no software and service independent.

If it's important, they'll call back

[Migraineman]

If it's truely important, the caller will re-dial after hanging up on your answering machine's greeting. Works fine.

Honestly, the "what about emergencies" arguement is as badly abused as "think of the children." My telephone is a resource for *my* convenience, paid for by *me.* If someone calls while I'm eating dinner with my family, the call is allowed to roll-over to the answering machine. If there's an immediate call-back, I'll probably interrupt what I'm doing. Somebody screaming into the answering machine in the next room would be a good clue too. Everything else gets done on *my* schedule.

It used to be that receiving a telephone call was a big deal - think back to the early 1900's. Nobody had phones. If somebody called you, there was probably large expense (money, time, effort) to place the call from the other end. That expectation persists to today, in spite of the ubiquity and low-value of most phone calls. The phone companies go to great lengths to maintain this perception of "high priority interrupt." They're in your face, and they want to stay there (but that's a completely different rant.)

Think of the children. They're busy eating their dinner and experiencing some family time. Call back later. (To address the original poster: get an answering machine; learn to use it; don't let the phone rule your life.)

No Problem

[Greyfox]

Pick up a Digium FXO/FXS card. Technically you only need the FXO module (The bit that plugs into the landline) but unless you have a SIP phone handy you'll need something to plug a phone handset into. You could try using a software-only phone but those things seem to be a bit of a pain in the ass. If you have more than one landline you can pick up a variety of combinations, such as FXO/FXO/FXO/FXS or FXO/FXO/FXS/FXS. The card I have supports up to 4 modules and you can mix and match modules to your heart's content. Note that you'll need to plug a plug from the power supply into the card if you plan to use the FXS module. This provides ring voltage to the FXS modules.

Slap said card into a Linux or Windows box. I chose Linux but it seems asterisk has been ported to Windows, too.

Now grab asterisk. If you went with Linux you'll have to download and install the Zaptel drivers for the Digium card, too. I haven't had much luck with the Debian packaged Asterisk and prefer to compile it from the CVS tree. Once you've got asterisk installed you can modify your extensions.conf file. Make some local extensions (You can use your FXS phone and a SIP soft phone like Linphone to test these.) Now you can do ALL SORTS of fun stuff. My home setup has a little voice menu system that asks you if you're a telemarketer and then asks you to dial 1 or 2 for myself or my room mate. If we don't pick up, the call goes into a voice mail system very simlar to what I have at work.

Eventually I plan to sign on with a VOIP service and keep the landline only for inbound calls and 911 service. You can also route local calls over a landline and long distance calls through a VOIP provider (or one of those 10-10 serivices if you prefer using one of those.) You can also set up speed dial keys for any combination (#1 on my phone gets you Abo's Pizza in Lafayette.)

I suggest that you keep an actual non-wireless phone plugged into one of the other landline ports in the house -- even if you're on a UPS, a protracted power outage could end up leaving you with no way to call 911. Having an old non-wireless phone around is the safest thing to do -- they draw voltage off the phone line to work, and that usually stays up. Just make sure you don't have to plug the phone into anything other than the phone line and you'll be good to go.

Asterisk takes a fair amount of configuring and it can be intimidating at first, but the flexibility it offers to the home user is unparalleled by anything else in its price range. For a home user, anything coming even close to it would be well out of the price range of most people.