PSTN access numbers are old-fashioned phone numbers that people can dial to reach VoIP phones. Typically the caller would dial an access number from a regular phone, then dial an "extension" (actually, the VoIP telephone number). Note: Neither the caller nor the callee needs to use SIP Broker.
The current list of PSTN access numbers that work with SIP Broker can be found here:
Note: ENUM (*013) is the default SIPCODE. In the above examples, you could dial 1-604-484-5289 or *013-1-604-484-5289 with the same results.