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# How do I handle anonymous calls without losing any leads?

Anonymous calls present a dilemma: most are spam or robocalls, but some are genuine leads who simply prefer not to share their number. 
Blocking all anonymous calls is easy, but it costs you those real leads.
The best approach is to route anonymous callers to a voicemail that asks them to call back with their number visible. 
Legitimate prospects will call back; robocalls and spam will not.

### Step 1. Open the Call Flow Builder

* Go to [Tracking > Call Flows](https://app.nimbata.com/tracking/call-flows).
* Click **+ Add** to create a new call flow.

### Step 2. Add the Caller ID Prefix filter

* Click the **+** button on the canvas.
* Select **Caller ID Prefix** from the Filters menu.

This creates two branches: one for the prefixes you define, and one for all remaining callers.

![](https://storage.crisp.chat/users/helpdesk/website/-/2/f/4/5/2f459a49cf382400/image_79bhgi.png)

### Step 3. Set one branch to catch anonymous callers

* In one of the two Caller ID Prefix path boxes, type **anonymous**.
* Leave the other path empty; it will handle all identified callers.

![](https://storage.crisp.chat/users/helpdesk/website/-/2/f/4/5/2f459a49cf382400/image_w5bwrj.png)

### Step 4. Route anonymous callers to Voicemail

* Click the **+** below the anonymous branch.
* Select **Voicemail**.
* Configure the voicemail greeting to ask the caller to call back with their number visible
* E.g. "We're unable to answer calls from withheld numbers. Please call again with your caller ID enabled."

![](https://storage.crisp.chat/users/helpdesk/website/-/2/f/4/5/2f459a49cf382400/image_18iudra.png)

### Step 5. Route all other callers to your destination(s)

* Click the **+** below the remaining-callers branch.
* Select **Dial** and choose the destination number(s) for identified callers.

![](https://storage.crisp.chat/users/helpdesk/website/-/2/f/4/5/2f459a49cf382400/image_1n2mr3r.png)

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🎉 Done. Anonymous callers hear a polite voicemail asking them to call back; genuine leads will; spam won't.

Detailed Guide: [**How to use the caller ID prefix filter for Geo-routing**](https://help.nimbata.com/en/article/how-to-use-the-caller-id-prefix-filter-for-geo-routing-5ptln6/)
Detailed Guide: [**How to block unwanted or spam callers**](https://help.nimbata.com/en/article/how-to-block-unwanted-or-spam-callers-1l5lrvu/) 
Detailed Guide: [**How to set up and listen to voicemails**](https://help.nimbata.com/en/article/how-to-set-up-and-listen-to-voicemails-ts6ehv/) 
Detailed Guide: [**How to assign tracking numbers to call flows**](https://help.nimbata.com/en/article/how-to-assign-tracking-numbers-to-call-flows-uxu7qb/)