One number multiple calls simultaneously, how is that possible?

So imagine a customer calls your office at the front desk and asks for a specific department or person but you only have one landline or business phone. All you can do is to share that department’s or person’s phone number on call or by text, doesn’t it sound unprofessional?

Most people would say to get a legacy intercom but those are bulky and ugly landline phones that occupy desk or wall space when everyone prefers to have a mobile phone. So how can an intercom service work on a mobile phone, the answer is VoIP or voice over IP and asterisk pbx that can easily go on any local or cloud server, it can be the same server hosting your erp, crm, website, blog, etc. No more ugly devices or need to pull telephone wires from conduits.

Our developer Amaya is kind of an expert when it comes to installing and managing asterisk. So she uses Airtel extreme fiber residential connection for her home. Now Airtel also bundles a VoIP service and landline number on the same fiber but different vlan ID 660 from internet which is 100.

Airtel uses different vlans so that they don't expose sip servers to the internet. Anyhow Amaya figures out the most of her sip config from router and password from geeky twins server. She then uses the config to create an endpoint in asterisk which is installed in her homelab server, which already has a local intercom configured, all she has to do is sip trunk to airtel and voila we get status O5 for successful authentication then after playing with extensions she was able to successfully enable incoming and outgoing.

Working extensions.conf

[from-airtel]
exten => _.,1,NoOp(Incoming Call from Airtel)
 same => n,Set(VOLUME(TX)=3)
 same => n,Set(VOLUME(RX)=3)
 same => n,Dial(${PJSIP_DIAL_CONTACTS(1001)}&${PJSIP_DIAL_CONTACTS(1002)}&${PJSIP_DIAL_CONTACTS(1003)}&${PJSIP_DIAL_CONTACTS(1004)}&${PJSIP_DIAL_CONTACTS(1005)})
 same => n,VoiceMail(1005@default,u)
 same => n,Hangup()
[internal]
; Internal calling: If 1001 calls 1002
exten => _100X,1,NoOp(Internal call)
 same => n,Set(VOLUME(TX)=3)
 same => n,Set(VOLUME(RX)=3)
 same => n,Dial(${PJSIP_DIAL_CONTACTS(${EXTEN})})
exten => *98,1,NoOp(Checking Voicemail)
 same => n,VoiceMailMain(@default)
 same => n,Hangup()
; Allow internal phones to dial out via Airtel
exten => _X.,1,NoOp()
 same => n,Set(VOLUME(TX)=3)
 same => n,Set(VOLUME(RX)=3)
 same => n,Dial(PJSIP/${EXTEN}@airtel-trunk)

Yes there are few quirks of this system and its end devices like voip phones and app tend to break sometimes, but for business we offer more sophisticated systems and services and better support.

Also on a side note it is encouraged to use vpn while connecting with sip server outside the local network for better security and encryption. 

Instead of using bulky legacy intercoms or manually sharing phone numbers, businesses can route calls to mobile devices using VoIP and Asterisk PBX. Developer Amaya demonstrated this by extracting SIP credentials from her Airtel Xstream fiber router, trunking it to an Asterisk homelab server, and successfully configuring internal calling, incoming ring groups, voicemail, and secure outbound dialing.