You cannot rely on a shelter being able to reach you until you have tested the route yourself, because three separate layers can stop the call: your handset settings, your carrier's network filter, and your voicemail box. A shelter may call from a switchboard, a kennel phone, or a number that looks unfamiliar, and any of those can be silenced, labelled as spam, or diverted before you hear a ring. Work through the layers below in order, then prove the fix with a real test call rather than trusting a settings screen.
Save the numbers that matter first
Start by building the contact list that a found-dog call could come from. Save your local shelters, the animal control office, your own vet, and the emergency clinics in your area, and ask each shelter which outgoing number it uses for owner calls, because a switchboard number may differ from the number printed for the public. Save every outgoing number you are given under a clear name, such as Shelter Kennels or Shelter Main Desk. Add a second household phone number to the record you leave with each shelter, so one silenced handset does not end the attempt to reach you.
Work through the three filtering layers
The first layer is the handset itself. Turn off any setting that silences unknown callers, check scheduled quiet or focus periods, and open the blocked list to make sure no shelter or clinic number has been added by accident after an earlier nuisance call.
The second layer is your carrier. Open the call-filtering controls in your carrier account or in its call-protection service, look for an allowed or trusted list, and add the shelter numbers there if the carrier offers one. Check the spam or filtered call log as well, because a call stopped at network level may never appear in your normal call history.
The third layer is voicemail. Open any separate spam voicemail folder, listen to messages that were diverted automatically, and check that your mailbox is not full, because a found-dog message that cannot be left is as lost as a call that never rang.
Prove it with a real test call
Settings screens tell you what should happen; only a test call tells you what does happen. Ask a shelter or your vet's reception desk to call you from the outgoing line they would use for an owner, at a time when you can watch the phone. Note whether the call rings with the saved name, rings as an unknown number, arrives labelled as spam, or goes straight to voicemail. If it is filtered, add that exact number to your contacts and to the carrier's allowed list, then repeat the test until the call rings normally. Test a text message too, and check your filtered messages folder if the text does not arrive in the main inbox.
While a search is active
If your dog is missing, loosen the filters further for the duration of the search: keep unknown callers able to ring, keep the ringer loud, and check the spam call log, the filtered messages folder, and the spam voicemail folder morning and evening. Tell anyone who shares your household what a shelter call might look like, so nobody declines an unfamiliar number out of habit while you are out searching. For that search window, KinsLe's Lost Pet Alert System adds a direct-message route alongside the phone call, so a member who finds your dog can reach you through the alert even while you are clearing a filter problem.