I think maybe you guys are onto something here and don't realize it, you're just not thinking it through.
In order to get Caller ID from the telco you're probably going to have to pay them for some extra service. This is one reason a lot of people are dropping landlines - it's a B.S. fee because the phone companies get Caller ID number information for free. Name lookups are a whole other matter (which is why Google Voice doesn't send them) but numbers are delivered on every call, and if you don't pay to receive them then the phone company just doesn't pass the information along to you.
But in some places, Caller ID is charged at 2 to 3 times the rate for any other "custom calling" feature. So here is a method that would likely work (though I don't guarantee it):
1) Make sure you have a Google Voice number that is a local call from your PSTN line. If you're not sure, you may be able to get the information from your telephone company, from tariffs on file at your state PUC/PSC (which in many states are available online), or from http://www.localcallingguide.com/
- or you could just place a test call from your PSTN line to your Google Voice number, then wait a month or two and see if it shows up on your phone bill as a toll call. This won't work if you don't have or can't get a local Google Voice number. Don't actually apply for a new Google Voice number (if you would need to) until you complete step 2.
2) Call your phone company and ask about Call Forwarding service. What you want to know is whether you have it on your PSTN line, and if so, is there a charge for each forwarded call. If they say yes and yes, ask if there is a way to pay a monthly charge to avoid the per-call call forwarding fee (which is often outrageous compared to the flat monthly charge that eliminates the fee). If they say no to the first, ask if you can get the feature and be sure to verify that if you pay a monthly charge, there will not be any per-call charges associated with using the feature. N.B.
If you are on a "measured" service line, where you pay for outgoing local
calls, you will pay the same rate for forwarded calls (even if you have to pay a monthly rate for call forwarding service), making this a far less attractive solution! If you can pay a flat monthly rate to get no-charge call forwarding, and you aren't on a measured service plan, then have them add the feature.
3) Once the feature is added to your line, set up call forwarding to forward all your calls to your Google Voice number. The phone company always sends the called number on forwarded calls, so Google Voice will receive it and send it to you, via your Google Voice connection on SP1 or SP2. For outgoing local calls you'll still use the LINE port to send them directly to the PSTN line.
Remember that many states give you a grace period to cancel an added feature without charge if it doesn't work as you expected it to.
If for some reason this won't work, you could try Plan B:
Go to http://www.telcodata.us/search-area-code-exchange-detail
and enter the area code and first three digits of your PSTN phone number and click the Search button. Note the company name (should be the phone company that provides your PSTN service), then note the "Rate Center". Click on the name of the rate center (NOT the actual words "Rate Center", but the NAME of the Rate Center in the column below) and you will get a list of all other companies that offer service in that rate center (in the Company column). If you are lucky, one of those companies may offer competitive PSTN service and they will throw in Caller ID for free (and possibly many other perks). Such companies can port your existing PSTN number and in some cases provide service over your existing landline, so as far as you're concerned nothing changes except the company you send your (probably lower) monthly payments to each month. Of course there are clinkers out there, so be sure you do a Google search on any company before switching over, so you don't find yourself doing business with the "telco of the damned" — I don't want you to be mad at me
for suggesting this. As with most other types of businesses, there are reliable competitive local phone companies and then there are a few real stinkers.
This assumes that you don't want to port your existing PSTN service over to a sip-based service. If you are willing to do that, and if you're not in a rural area and/or served by some small independent telco, then there may be additional options available to you by using a VoIP provider that allows you to "Bring Your Own Device", or one of the companies supported in the OBiTALK portal. I don't think I've ever heard of a commercial VoIP provider that charges extra to deliver Caller ID, and many of them can port existing telephone numbers.