Hi Rachel,

Yes, you are right on the money with the Alternate extension idea :)

You can setup the Mobile# as an Alternate Extension for the Subscriber mailbox. Have a look;

Setting Up Alternate Devices

In addition to your primary extension, your Cisco Unity administrator may set up alternate extensions for you, and may also allow you to do so in the Cisco Unity Assistant. Administrators set up alternate extensions for various reasons, such as handling multiple line appearances on subscriber phones or simplifying message addressing for subscribers on different Cisco Unity servers.

***You may want to use alternate extensions to make calling Cisco Unity from an alternate device, such as a cell phone, a home phone, or a phone at another work site more convenient. When you specify the phone number for an alternative device in the Cisco Unity Assistant, Cisco Unity handles all calls from that number in the same way that it handles calls from your primary extension (assuming that the alternate phone number is passed along to Cisco Unity from the phone system). This means that Cisco Unity associates the alternate phone number with your account, and when such phones are set to forward to Cisco Unity, callers can listen to your greeting, and leave messages for you, just as they would when dialing your primary extension.

Depending on how Cisco Unity is set up, you may be able to use the Personal Preferences page in the Cisco Unity Assistant to:

View the alternate extensions that your Cisco Unity administrator specified for you.

Specify phone numbers for up to five alternate devices, in addition to those that your Cisco Unity administrator specified for you.

Do the following procedure to set up alternate devices in the Cisco Unity Assistant.

To Set Up Alternate Devices

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Step 1 In the Cisco Unity Assistant, on the Preferences menu, click Personal.

Step 2 In the Alternate Devices table, enter an extension up to 30 characters in length in the Number field.

When entering numbers in the Alternate Devices table, consider the following:

Each alternate extension that you add must be unique; Cisco Unity will not accept an extension that is already assigned to another subscriber (either as a primary or alternate extension) or to another Cisco Unity entity (such as a public distribution list).

Enter digits 0 through 9. Do not use spaces, dashes, or parentheses.

Step 4 To specify another device, click the Add Row button and repeat Step 2 and Step 3.

Step 5 Click Save. The alternate devices you specified are enabled for all rows in the table.

Then you also use the:

In the*** "Prompt for Phone Password"*** section, check the "Only When User Calls From Unknown Extension check box".

So that Unity Prompts for Phone Password when the number calling into Unity is not recognised.

Hope this helps!

Rob