2. Phone number formats

In general, NFON accepts the transmission of phone numbers in all fields (FROM, TO, P-Asserted Identity, P-Preferred Identity) in the following formats:

Country Code SIP format
+49 <sip:+49894531234@trunk.cloud-cfg.com>
0049 <sip:0049894531234@trunk.cloud-cfg.com>


Phone number transmission

Incoming phone number formats are always in the international format with leading 00.

Phone number transmission (outgoing customer to NFON)

In case of outgoing calls, NFON offers two options for transmitting the phone numbers:

  1. The SIP account can be placed in the FROM USER field and the valid phone number will be displayed in the FROM DISPLAY field
  2. A valid phone number is displayed in the FROM USER field and in the FROM DISPLAY field

In addition to the formats accepted under the section Phone number formats NFON does allow the following local number formats as caller ID (B-number, destination number)

Local number format SIP format
Telephone number without local area code (LAC) <sip:4531234@trunk.cloud-cfg.com>
Telephone number with local area code (LAC) (089) <sip:0894531234@trunk.cloud-cfg.com>


Phone number suppression (anonymous calling) - CLIR (Calling Line Restriction)

The caller ID can be suppressed (anonymous calling) for an outgoing call by two

  1. Setting the FROM Display field to anonymous
  2. Setting the Privacy header to id

Please find examples in chapter D.

A phone number associated with the trunk must always be set in the P-Asserted Identity header in a format as described above in order to process the call correctly.

CLIP no screening

In order to transmit a 3rd party phone number, not associated with the trunk, the "Clip no-screening" setting must be enabled on the trunk. Otherwise, only the associated numbers can be transmitted for outgoing calls.

Once the trunk allows transmission of 3rd party numbers, the desired phone numbers must be set in the P-Asserted-Identity header of the INVITE in a number format as described above. If no P-Asserted Identity number is set, NFON will determine it independently and insert it in the INVITE field.