“Internal Prefix” cannot be left blank (iOS v6.0.0.0)

[takayuki-nakano]

Summary

In iPhone Linphone v6.0.0.0, the Internal Prefix field in account settings cannot be left blank.
This makes it impossible to place external calls in our PBX setup, because any prefix automatically added to dialed numbers causes calls to fail.
In previous versions and in Android v6.0.17, Internal Prefix can be left empty.

Steps to Reproduce

1. Install Linphone v6.0.0.0 on iPhone.
2. Add a SIP account.
3. Attempt to clear the Internal Prefix field (leave it blank).
4. Save settings.

Expected Behavior

It should be possible to leave Internal Prefix empty, matching Android behavior and previous iOS versions.

Actual Behavior

The field is required; a value must be entered.
Any added prefix breaks external dialing in our PBX environment.

Notes

• Android v6.0.17 allows blank Internal Prefix, works fine.
• This issue did not exist on iOS Linphone v5.x.

Environment

• iPhone: Linphone v6.0.0.0
• Android: Linphone v6.0.17 (for comparison)
• SIP Server: [briefly describe your PBX or SIP platform]
• Network: Internal LAN / VPN
• Impact: Unable to place external calls from iOS client in production.