You are asking a very loaded question. I guess it depends on what your definition of "successfully" is.
Any "unsupported phone" would most likely have to be manually configured, which means that the user has to have a good working knowledge of the se,t and is hopefully able to get many functions, beyond the basics to work.
This is something that you might attempt on a handful of sets, perhaps in a home environment, if you already have them, and are prepared to spend some time working on this.
While most SIP capable set will probably work on 3CX for the basic functions, most 3CX users want to do a professional install at the request of a client, with the least hassle, and in the least amount of time, so they will stick with something supported, that can be auto-provisioned. You don't want to install unsupported phones and then receive trouble calls every week because something is not working.
If you have a specific set in mind that you are trying to get working, then list it, and someone may be able to offer assistance. The forum is full of people doing just that.
Don't go out and buy a lot of unsupported sets because someone told you that they will (may) work on 3CX, stick with what is known to work.