If you can both receive and place calls with all other destinations fine, the problem is likely on your friend's end.
See here for an example:
viewtopic.php?f=8&t=19773.
A) Note that only one registration per FPL account is allowed at any time. When there are multiple devices/softphones using the same account, only the most recent registration is valid. The previous device will lose registration and incoming calls will not work on it. This is especially important to consider if someone else is using your friend's SIP credentials (username and password) that are found after logging in at
https://www.freephoneline.ca/showSipSettings (or if she is trying to register her FPL account with a smartphone SIP app or with another device).
Registration is required for incoming calls. It is not required for outgoing calls. Your friend needs to log in at
https://www.freephoneline.ca/showSipSettings to check SIP Status and SIP User Agent. SIP Status needs to show connected. SIP User Agent needs to reflect the device she's using (her ATA) and not something else.
B) Ensure SIP ALG (pay close attention to #2 below) is disabled in the router or modem/router combo your friend is using. Alternatively, she can use voip4.freephoneline.ca:6060 for the proxy server.
If your friend wants help, she needs to provide
i) the brand and model of her modem,
ii) the brand and model of her router,
and
iii) the brand and model of her ATA or IP Phone.
---
(Generic info)
Typically, for VoIP SIP services, especially for freephoneline, you want
1) a router that does not have a full cone NAT,
Visit
https://www.think-like-a-computer.com/2 ... es-of-nat/.
Mango from the Obitalk.com forums writes,
“Use a restricted cone NAT router, and do not use port forwarding or DMZ. Restricted cone NAT will only permit
inbound traffic from the service provider you're registered to. If you have a full cone NAT router, it will allow traffic
from any source. This is probably not what you intend.
If you have a Windows computer, you can test your router using the utility here:
http://www.dslreports.com/forum/remark,22292023. To run it, use stun stun.ekiga.net from a command prompt.”
Essentially, you download the stun-test.zip file; extract the stun.exe file from within the zip file to an easily
accessible location; use an elevated command prompt (visit
http://www.thewindowsclub.com/how-to-ru ... inistrator); change directory (cd) to the
directory or location where you extracted stun.exe (visit
http://www.digitalcitizen.life/command- ... c-commands); and type “stun stun.ekiga.net” without
the quotation marks followed by the enter/return button on your keyboard.
Asus routers, at the time of this writing, produce port restricted cone NAT routers, for example and are fine,
provided you’re using one with Asuswrt-Merlin, third party firmware installed.
2) a router that lets you disable SIP ALG if it's buggy,
To understand why SIP ALG often causes horrible problems, please visit
https://www.voip-info.org/routers-sip-alg/ (scroll down to the section on SIP ALG problems).
If you're dealing with a modem/router combo issued by an ISP or a router with SIP ALG forced on, you may have
to use voip4.freephoneline.ca:6060 for the Proxy Server. The purpose of voip4.freephoneline.ca:6060 is to circumvent
faulty SIP ALG features in routers.
3) a router that allows you to set QoS or assign highest priority to your ATA or IP Phone over all other devices on your LAN (local area network),
For a very general description of what QoS can do for you, visit
https://www.voipmechanic.com/qos-for-voip.htm.
The basic idea is if you're torrenting or have a bunch of other computers, smartphones, tablets, etc. downloading and uploading (hogging all your available bandwidth), you don't want
your ATA not to have access to enough bandwidth to make or receive calls properly. So QoS or a Bandwidth Monitor feature (which is just another form of QoS) is a really good idea for VoIP users.
I often get an occasional relative complaining to me, "Hey my calls sound choppy." And then when I go visit, some kids are playing MMOs on a computer, while another person is downloading a huge file,
and another person is backing up files to a cloud service all at the same time someone else is trying to talk on the phone. All those devices, without QoS enabled, are fighting over available bandwidth along with the ATA.