Whenever you have friends in Hong Kong, you need to need to chat with them very often. You can consider to subscribe the service "HKBN 2b App" via your mobile phone (iPhone and Android) for HKD 28 per month (around USD4 / month). HKBN 2b will provide you a Hong Kong 8-digit telephone number such that you can use it for both outbound and inbound calls.
You need to renew it monthly or more using the HKBN 2b App software for HKD28/month. Once you receive the SIP credential, you can put them on OBi device, as follows :
Service Provider Proxy Server s2hkbntel.net
Service Provider Proxy Server Port 5060
Outbound Proxy Server 18.104.22.168
Outbound Proxy Server Port 5060
User Name XXXXXXXXHK