I am in the process of getting a podcast together and it would involve taking audio from the phone lines. My audio isn't as important because I can record it just fine in my studio. I mainly want the callers audio to be good from their end.
 
Some podcasts will do a co host show and the person who isn't in the studio will drop box a better recording to the studio. If they use Skype they might use it to line up the two audio tracks. I won't be doing this because I don't have a co host and because I don't want to require my interviewees to email me audio every time I talk to them.
 
I know people use Skype or the Google equivalent but basically most serious podcasters seem to use something like a Zoom recorder to record the audio and then they upload from SD card to computer and work with the audio. This eliminates all of the issues involved with lag time, computer noise and the unexpected computer glitch. I think it makes sens,avoids voip all together and keeps everything to a simplistic minimum. When using a zoom to record they also use a mixer to put one channel back through so the listener can hear the other person.
 
I know there are expensive specialty items for this but I don't want to spend ton of money on this and most of those won't work because they deal with an old analog phone line and I have my phone through my cable company. The cable company has a modem with a phone jack on it and I don't believe it works in the same way or would work with many of those other options.Plus I use cordless phones.
 
Here is an idea I had and I am open to comments or suggestions.
 
I get a phone system with multiple handsets from the same base . These handsets are capable of using a plug in headset. I take one handset and use that as my phone while also recording on my studio mic. I take another handset and use that as the phone to output the other persons audio. The only part of the output jack I would use from that handset is the audio out from the caller. I dial the show guest and soon after connection is made I put the second handset online and put that audio into my Mackie mixer to boost the signal and then forward it into a zoom recorder on one channel. I also take my audio into the same mixer and run it into the second channel of the zoom. 
 
I looked at the output jack on the phone handset I have and it is smaller than the typical 3.5mm found on most cell phones. I'm not sure about the impedences. I can get an adapter to take it from the smaller phone jack to a standard 3.5mm and I have a connector goes from 3.5mm to RCA L/R.  Any thoughts?
 

Jk audio

If you are talking landlines it is better to retrieve the signal from the phone line itself using the right gear though. You need a thing called a Hybrid. It essentially isolates the audio component and sends it out a separate output that can be used in studio and recording situations.
 
You can make one too as I did mine. It is bascialy a decent quality 600 ohm 1:1 transformer fed with a cap in series to remove the DC component on the phone line. The secondary winding can be used as the isolated output. Both conversations will appear on the audio line. (Yours (sidetone) and the other person that is)
 
As Mike says JkAudio seem to be in the business of providing such hardware.
 
The handset probably has a 2.5 mm connector on it. You could also start by trying a lead from that to 6.5mm jacks etc for the mixer end etc.. The signal might be OK there as well.

Is JK Audio still around??? I still have probably half a dozen of their gizmos in an old tool kit somewhere. No self respecting broadcast engineer would leave the building (or enter if for that matter) without a couple.
 
Jeff's description of a transformer with a blocking capacitor will work, but you will end up with both sides of the line. If you need to record both side that's great, if you can guarantee that no one on your side will speak it also works. And it is cheap!
 
A better solution is a "Wheatstone Bridge" (not to be confused with Wheatstone the audio manufacturer, although I am certain there is a connection there<G>). You can also build this, and it is the heart of the hybrid that was mentioned. With a bridge or a hybrid you can actually separate the two sides of the conversation and record them onto separate tracks - which is very often helpful.

My two favorites are the Symetrix TI-101 (later sold by Radio Systems) and anything from Gentner (who later became Clearone). I have a Symetrix TI-101 and Clearone TH-1 in my studio - they both work quite well. If I had to pick one I'd probably pick the TI-101, but I also have a couple other Clearone XAP boxes (they are used for audio conferencing, and are a lot of fun to play with), so I keep the TH-1 around. You can find both of these on eBay for very reasonable prices, and it is a lot easier than building one<G>!
 

Thanks guys for your suggestions! 
 
Jeff, using the "right gear"  as you say is what I really wanted to do in the beginning and it's what I knew I should do. Since I already had the phone I figured maybe I could make use of it effectively. I think my idea for using it probably would have worked in the way I described but that whole thing would have been a band aid approach to the problem. I also checked out some of the JK gear Mike mentioned and it isn't terribly expensive.
 
I could  build something simple for the purpose, you all had some good recommendations on that, but when I seen the thing wst3 mentioned...the Symetrics TI-101 and looked at it.....that looks like the kind of thing radio stations use. It looks well built and it has  lots of capabilities. I was afraid of the cost and went to eBay to check it out......long story short I seen a deal I couldn't pass up and it should be at my house in  few days! I appreciate the help in finding something.
 
The thing is....I'll be using this a  lot,so I don't want something flimsy. I'm very happy with this choice. My only concern is my phone system. I take my phone feed off of a cable modem and I think it has jacks for two phones. In theory at least, I should get the same thing at the jack that you would get from any analog phone jack, otherwise how could a  typical home phone either cordless or not be cross compatible? Unless something in the phone or modem recognizes a difference and makes an internal change. I can plug any kind of phone into that jack as far as I know. The fact that it went through a  D/A conversion process across my cable system shouldn't matter. I hope I'm right about this....if not I'll be reselling this item.

My concept is rather crude but it does work as I found most of the time you want both conversations. But what Bill has suggested is difinitely better. It was interesting to see how many of those Symetrix units are for sale as well. They seem pretty good. You will be able to null out the unwanted conversation and record the two sides to the conversation separately which will be better in the long run. It also means you can feed your studio mic into the system as well and ultimately down the line too. Hope it all works out.

Thanks Jeff!

JK is still around, Sweetwater carries what you want, look for the QuickTap

Starise
I take my phone feed off of a cable modem and I think it has jacks for two phones. In theory at least, I should get the same thing at the jack that you would get from any analog phone jack, otherwise how could a  typical home phone either cordless or not be cross compatible? Unless something in the phone or modem recognizes a difference and makes an internal change. I can plug any kind of phone into that jack as far as I know. 

Tim, the #2 jack is only active if you have a second phone line with a separate phone number.
You can use a simple dual outlet/splitter plugged into the #1 jack.
 
Yes, the phone jack is effectively just like a normal pots jack, even though the modem is using voip.
 
A good signal is critical for you, and phone/internet is particularly sensitive to signal issues.
If your cable provider is Charter, I can check it from here (I'm a Charter tech). If you are using Time Warner, have customer service test it. They can see the same thing I can in their own system.

I guess because it's cable the ringer voltage would not be an issue... 
The voltage that makes an old school phone ring is around 90 Volts AC, not something to mess with in an audio circuit.