Entering phone numbers using non-Arabic numbers results in a validation error in the Microsoft Lync Client. What should I do?

The phone's input language is used for all fields in an application. It is not possible to use multiple input languages at the same time within an application. Exit the Lync application and change the phone's input language to English (or any language that uses Arabic numbers). Return to the Lync application and enter the desired phone number(s). The phone's input language can then be changed back to the desired language.