Hi,
As per my understanding, office 365 A4 plan says Lync voice on-premise , means you can deploy Lync server voice features like PSTN inbound/outbound call, PBX integration etc at on-premise network. Currently, PSTN calling features isn't available
on Lync-online. As you know, PSTN usage isn't free and you may need to work with provider on the costing part.
Here is the link for office 365 forum ;
http://community.office365.com/en-us/f/163/categories.aspx
Thanks
Saleesh
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