I am assuming that since no one has responded to this question that they have not been a problem for those growing them.

I had hopes that someone would post a response to this. I'm questioning this in my own yard. I moved what I believed to be all of a calla, then had trouble getting out the remains. Every spring for about 4 years, I would dig out the new plants and put the surrounding soil through a colander in search of roots etc. I ended up solarizing the whole bed for a year.

I don't know alot about callas but I would not consider them invasive. My wife bought some about 5 years ago and planted them in a bed in the front yard where they were in full sun all day. I moved them 2 years ago to a bed where they receive more shade and they are more happy there. I have not had any grow back in the bed out front. They are blooming more and I have about 15 to 20 seed pods. I am going to wait until they are mature and then cut them off. I will probably plant some in pots and give the rest away but I don't want to leave them in the bed because I don't want a bunch of calla babies growing there. I do the same thing with the Arums and Arisaemas I grow.
Jim