This issue occurs when the call is from a public switched telephone network (PSTN) number.
Resolution
To resolve this issue, install the following cumulative updates:
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2988177 August 2014 Cumulative Update for Lync Phone Edition for Aastra 6721ip and Aastra 6725ip telephones (KB2988177)
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2988178 August 2014 Cumulative Update for Lync Phone Edition for HP 4110 and HP 4120 telephones (KB2988178)
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2988181 August 2014 Cumulative Update for Lync Phone Edition for Polycom CX500, Polycom CX600, and Polycom CX3000 (KB2988181)
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2988182 August 2014 Cumulative Update for Lync Phone Edition for Polycom CX700 and LG-Nortel IP Phone 8540 telephones (KB2988182)