Using virtual phone numbers for calls and texts via Session Initiation Protocol (SIP) using LINPHONE and /e/ OS (Android)

1 Introduction

After having happily used a custom Android OS called /e/ OS [1] for several years with refurbished Samsung mobile phones, my provider COMVIQ (Sweden) has now at the beginning of December 2025 switched off its G2/G3 mobile phone networks [2], leaving only G4 and G5 activated. As a consequence, I cannot make or take calls anymore (“network busy” error) and only receive but not send SMS texts.

After feedback from the /e/ OS community [3, 4, 5], it seems that to talk via G4/G5 the voLTE (Voice over LTE) module needs to be activated, ideally while still on a G2/G3 network, which I was not aware of. It can also be activated on the G4/G5 network but only with the original Samsung Android OS because of propriety, customized code. Since I did not want to convert to the Samsung Android, I tried to replace the missing Call+SMS services with a virtual number with VoIP (voice over IP) with the following required features:

  • Priority 1:
    • incoming calls
    • outgoing calls
    • incoming SMS
    • outgoing SMS
    • reasonably priced < 6EUR/month (serving private users for casual use, not only large businesses for call centers)
    • trustworthy provider (no scammer, cf trustpilot.com)
    • reliable, good quality services (technology, support)
    • Swedish mobile phone number (although I considered also other european phone numbers as second Choice)
    • phone app which works with deGoogled Android OS, ie /e/ OS v3.3 (microG services)
  • Priority 2:
    • provider located in Europe (non-US, non-UK, non-IL)
    • serves private users, not only large businesses

2. Considered Providers

It turned out to be difficult to find a provider which did not suck. I have researched the following providers [11]:

  1. voipvoip.com (owned by Zadarma.com)
    1. Pros:
      1. reasonably priced
      2. supports Swedish mobile numbers
    2. Cons:
      1. allows only to send SMS with standard text messages from default sender “TEAMSALES”, which basically makes sending SMS unusable
      2. Zadarma App did not work under /e/ OS, no notification windows for calls
  2. zadarma.com (owns voipvoip.com)
    1. Pros:
      1. owns voipvoip.com, reasonably priced
    2. Cons:
      1. no registration possible, did not accept my email addresses *@protonmail.com, *@pm.me, *@murena.io, @e.email
      2. Captures for logins were very annoying
  3. sonetel.com
    1. Pros:
      1. Swedish, reasonably priced, Android app
    2. Cons:
      1. incoming calls did not work
      2. Validation of ID requires loads of documentation
  4. blacktel.io
    1. Pros: very cheap
    2. Cons: scammer according to trustpilot
  5. moremins.com
    1. Pros: very cheap
    2. Cons: no Swedish mobile numbers, scammer according to trustpilot
  6. vnumbers.com
    1. Pros: trustworthy, reasonably priced
    2. Cons: strong ties to US/Israel
  7. https://46elks.se
    1. Pro:
      1. Swedish, friendly support, reasonably priced
    2. Cons:
      1. supports mostly developers and programming APIs with call and SMS
  8. voip.ms
    1. Pro:
      1. provides numbers also to individual customers
    2. Cons:
      1. US-based with ID verification using PERSONA

Finally, ended up signing up for an account with a virtual mobile phone number with VoipVoip.com for in total 47USD (6USD setup fee + 12*3USD/month +5USD pre-paid).

2. Considered Apps

  1. ZADARMA
    1. Pros: Official ZADARMA/VoipVoip App
    2. Cons: does support incoming calls, because it needs Google Mobile Services, which are not fully available and supported by microG services on /e/ OS.
  2. LINPHONE
    1. Pros: Open-source, user-friendly, does support incoming calls and notifications!!!
    2. Cons: interference with other installed SIP apps

Other apps I tested are Zoiper, Softphone, SipDroid, Sinetic, … but LINPHONE clearly sticks out as most user-friendly and functional.

3. Instructions

  1. Install LINPHONE app only and no other apps, not even ZADARMA app
    Note: Multiple SIP apps can interfere with each other, eg if passwords or other configs are updated, still “holding” the registration and causing authentication issues (eg, falsely stating that login or password was not matching).
  2. Use the SIP settings of your VoipVoip Account from this page [7]
    Note: The font makes it hard to tell the difference between “O” (capital letter O) and “0” (Number Zero) and “I” (capital letter I) and “l” (lowercase letter l). To avoid typos in your password, choose a password without these letters or copy & paste the password to a document and set to a non-ambiguous font, eg Courier New or Fira Sans Mono
  3. Configure LINPHONE app with Account settings of your VoipVoip SIP Account according to this tutorial [6]
  4. Configure LINPHONE app to integrate with Android OS
    1. Go to LINPHONE > Settings > Advanced Settings > Start when device boots: ON
    2. Go to LINPHONE > Settings > Advanced Settings > Keep app alive when using service: ON
    3. Go to LINPHONE > Settings > Calls > Calibrate echo canceller
      Note: I experienced loud and clear sound, but the person I called reported hearing themself with an echo.
  5. Configure Android OS to integrate with LINPHONE (if not already per default):
    1. Use Path to LINPHONE app info:
      1. Option 1: Android Settings > Apps > Linphone
      2. Option 2: LINPHONE > Settings > Advanced Settings > Linphone Android Settings
    2. Set Notifications >All Linphone notifications: ON
    3. Set Permissions:
      1. Allowed (Camera, Contacts, Microphone, Notifications),
      2. Not allowed (nearby devices),
      3. Pause app activity if unused: OFF
    4. Set Mobile Data Usage:
      1. Allow Network Access: ON
      2. Wi-Fi Data: ON
      3. Mobile Data: ON
      4. Background Data: ON
      5. VPN Data: ON
      6. Unrestricted data usage: OFF
    5. Set App  battery usage:
      1. Allow background usage: ON
  6. Replace your old mobile phone number by configuring call forwarding to your virtual mobile phone number for all calls.

4. Problem solving

The following issues may arise:

  • Contact helpdesks:
    • Your mobile phone provider, eg COMVIQ (Sweden) in my case [8]
    • Your SIP provider, eg VoipVoip.com in my case [9]
    • Your SIP app developer or community, eg LINPHONE in my case [10]
    • Your ANDROID OS developers or community, eg /e/ OS in my case [3,4,5]
    • Use AI assistants for bug tracking and solutions
  • Authentication issues (login or password not matching)
    • Refresh web pages of VoipVoip SIP settings
    • Check all other SIP settings, eg selecting TLS instead of UDP protocol may cause this issue
    • Deinstall all other SIP apps on mobile phone (Android) or laptop (Linux, Windows), which may hold a SIP connection using old authentications credentials
  • Echo in the line: Go to LINPHONE > Settings > Calls > Calibrate echo canceller
  • No connection: SIP does not work on EDGE (G2.75) mobile networks.
  • Echo Test call for VOIPVOIP SIP account: call 4444, speak and listen to the echo of your own voice.

4. Conclusion

I have successfully replaced the disfunctional COMVIQ mobile phone number with a VOIPVOIP virtual mobile phone number to make and take phone calls. Although the VOIPVOIP virtual phone number only supports receiving SMS (not sending customized SMS), this is not an issue any longer, since after some interaction with COMVIQ customer support, sending and receiving to the original COMVIQ mobile phone number started working again. Mission accomplished.

Links:

[1] https://e.foundation

[2] https://www.comviq.se/nedslackning-2g-3g

[3] https://community.e.foundation/t/sip-calls-not-ringing-not-shown/78518

[4] /e/OS & Murena – community support [Telegram], https://t.me/+HYMdK0PkIUdlZWZk

[5]  https://gitlab.e.foundation/e/backlog/-/issues/9113

[6] https://zadarma.com/en/support/instructions/android/linphone/

[7] https://my.voipvoip.com/mysip/

[8] https://www.comviq.se/hjalp/kontakta-oss

[9] https://my.voipvoip.com/tickets/ with online chat

[10] https://www.linphone.org/en/contact/

[11] https://www.guru99.com/best-sip-trunking-providers.html

 

http://wilmarigl.de

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