Sometimes you come across a situation when an SRV record cannot be created either externally on internally (for whatever reason)

Don’t despair as the clever folk at Microsoft development have implemented additional options should Lync Communicator fails to reach the Lync FrontEnd Server by means of the SRV record.

Discovery options are as follows:-
1. SRV
2. sipinternal.
3. sipexternal.
4. sip.

So by simply adding an A record as above and pointing it to the Edge Public interface (where the Access Edge role resides) you can get around using SRV. Do keep in mind that this will add a few seconds to the logon process.

Also keep in mind that some third party vendors have created product that uses SRV records to log in, of course these may need consideration.