Do I get full conference call management options on iPhone 6 model A1549 if using it with GSM carriers?

Question

I have iPhone 6 model A1549, bought from and currently using with Verizon. You all must be aware that we can use the same phone for GSM carriers like at&t as well. Now we all know that some of the features related to conference calling are not available on CDMA carriers, like we cant have more than 2 callers, and we can't manage conference calls by making the conversation with one party private for some time and again switching back to conference mode, disconnecting a particular party instead of having to end the entire call etc. reference link- iPhone: Understanding phone features - Apple Support These features are available on GSM models and carriers, I just wanted to ask if I use a GSM SIM from a GSM carrier on this model, do I get these additional conference call management options or I am restricted to Verizon like experience while being on at&t (and while using the at&t SIM in this model)

Answer 1

Yes, I am dealing with this right now on at&t with a 6 plus. I've been down the same road as you. I got it to work with a windows phone yesterday but not my 6 plus when I switched back to the iPhone. My wifes 6 works fine. I believe it is an at&t issue and not an 8.3 issue. After dealing through several levels of support at at&t, they are telling me it has to do with their transition to hd voice. Some people are having this issue because they are updating their system and some peoples phone profile, on phones that have hd voice capabilities, are not getting added to their line and call forwarding will not work without it. I have a trouble ticket open to their engineering dept and they promise it will work for me on or before the 24th of april. Engineering has to build my phones profile so call forwarding will work with my iPhone.
This is frustrating because like you, I need to forward my calls because I have no signal in my office and need to forward to another phone so I can get my calls. If at&t would quit dragging their feet and enable wifi calling, this wouldn't be an issue for me. I would suggest you put more pressure on at&t and escalate this until it gets resolved. Or put your sim in a phone that does not have hd voice capability and see if it works then.
Good luck. I'm keeping my fingers crossed this will be fixed for me on or before the 24th. We'll see.
EDIT: I see you did put it in another phone and it worked. That backs up that the issue is at&t and their hd voice upgrades. They had no explanation as to why some work and some don't, but have them make sure a profile for your phone is on the line. If not, they'll need to build one for the phone so that it''l work. At least that's the story for now. Like I said, I'll know more in a day or two.