I have not had any success with it and I am also in zone 5 Wisconsin (Dodge county), BUT I have also never had a volunteer tomato grow in my yard. A friend of mine just a bit further south and east (Milwaukee county) has had numerous volunteers (but he never tried winter sowing).

So, I would say it is something you will just have to try to see how it goes for you. You can probably stack the odds in your favor a bit by not sowing in Dec/Jan and maybe waiting until March so the worst cold of winter is passed.

Interesting idea. I do agree that volunteers of all kinds really seem to take off, I guess same would be true for winter sowing.
Most volunteer tomatoes I get are cherry type. Maybe I'll try it too.

Wherever I have grown tomatoes (since I rotate the crops) I always have a few volunteers pop up from the previous year. I haven't let them go full bore or transplanted them to see what happens yet. When I started gardening 4 years ago I was given 3 volunteers and they beared some fruit, but not as much as ones that were bought or started indoors. Not to say that they couldn't be as productive as long as the proper amendments are given early and they are nurtured.

I did successfully winter sow some tomatoes. I did it in milk jugs. Placed the jugs on the south-facing stone wall of my barn. They sprouted very early, then we had a wicked freeze and they were toast. I knew I should have moved them in to the garage over night, but I was too lazy. Lessons learned...