I have caller id service with my phone company; Why does my Radio Shack heavy duty wall phone with caller id display all rows of 8's in the caller id area?

It may be enabled, but normally you have to pay for it.

Page 54 of the manual. It is automatic.

Using Caller ID service
Important: This unit is Caller ID compatible. To use Caller ID features, you must subscribe to a Caller ID service. Contact your service provider/telephone company for details.

https://help.panasonic.ca/viewing/ALL/KX-TG9581/OI/TG9581_PNQX6371ZA/TG9581_PNQX6371ZA.pdf

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Please call your phones service provider, they may charge for this service. Just because the phone is capable of caller ID function doesn't mean it is a free service.

You'll have to contact the vendor, I'm afraid.

• Did you fully charge your phone? - Make sure you fully charge for 16-24 hours .
  
  
• Is the battery old? - Replace the battery.
  
  
• Is the electrical outlet switch turned on? - If you are using AC (electrical) power, make sure that the unit is connected to a non-switched electrical outlet.
  
  
• Are the connecting wires tight - Unplug the AC power converter from the unit and plug it back in.
  
  
• Do you have Caller ID service with your telephone company - In order to receive Caller ID records, you must subscribe to the standard name and number Caller ID service available through your local telephone company. If the Caller ID works for normal calls but not on Call waiting calls, then you must contact your phone company to get the combined CID/CW service.
  
  
• Caller ID shows up after second ring - Be sure to wait until the second ring before answering. Caller ID signals comes through after the first ring, if caller pick ups phone too soon Caller ID signal will not be transmitted to the handset.
  
  
• Confirm that caller ID is still working on that particular line by checking another phone on the same line - If Caller ID is not coming through contact your phone company provider.
  
  

If this does not fix your problem, contact your authorized Service Center.*

Maybe you forgot to sign up with the telecommunication for caller id

Please download this manual, and study e.g on page 21 About caller ID If you subscribe to caller ID service from your local telephone company, this feature displays the name and telephone number of the caller before answering a call (even when you are on another call). The caller ID features of this product will work only if you subscribe to caller ID service and both you and the caller are in areas offering caller ID service, and if both telephone companies use compatible equipment. Contact your local telephone company if: • you have both caller ID and call waiting, but as separate services (you may need combined service), • you have only caller ID service, or only call waiting service, • you do not subscribe to caller ID or call waiting services but wish to try them. There may be fees for these services, and they may not be available in all areas. This product can be used without subscribing to either caller ID or combined caller ID with call waiting service, although the caller ID features of this product will not function.
http://www.vtechphones.com/docMgt/public/art/52882/6041_manual.i4.pdf

Buy a cordless phone that has caller ID and if you don't already have caller ID service you need to order it from your phone company.Most every new cordless phone has caller ID

You're right, at least one of them should. You should contact your telephone company and ensure you have Caller ID while on Call Waiting service (CIDCW) - it's not always the same as just Caller ID. Sometimes they'll want even more money. :)

Is the phone FCC approved for use in the US? Does the model purchased in Singapore use the same Caller ID algorithm as US phones? Have you tested a known good caller ID capable phone at your location to make absolutely sure the caller ID is actually turned on?

just connect one end of the phone plug to the id caller,then connect the outlet of the caller id and fix it to phone...........even then if u hav problem, may be ur caller id doesn.t hav batteries..............otherwise u may hav some problem in the id caller socket where phone plugs r inserted................