Try to always choose the closest server to your physical location, to try to keep latency at the minimum.
For numbers in North America and Central America: sip:inbound-us-east.toky.co:5060
South America: sip:inbound-sa-east.toky.co:5060
Europe and Africa: sip:inbound-eu-west.toky.co:5060
Western Asia: sip:inbound-eu-west.toky.co:5060
Central Asia and Asia Pacific region: sip:inbound-ap-sg.toky.co:5060
Australia and New Zealand: sip:inbound-ap-au.toky.co:5060