Here's a couple of those winter indoor tomatoes threads imafan was talking about:
http://www.helpfulgardener.com/forum/vi ... es#p369335
http://www.helpfulgardener.com/forum/vi ... es#p363089
As noted, tomatoes are annuals and will reach the end of their life span; they cannot just produce tomatoes year round. But you can start tomatoes from seed in late summer and then bring them in for the winter (IF you have the proper light set up and are willing to work pretty hard at it). If all goes well, they will produce some winter tomatoes for you (what a luxury, home grown tomatoes in dead of winter). Then in late winter you can start more seeds indoors under lights, to have new plants ready to take outside when it is warm enough in spring.
This will still not guarantee you year round tomatoes, but doing it that way where I am, one could eat home grown tomatoes maybe as much as eight months of the year. For really year round tomatoes, you would have to start seeds more than twice a year, which would mean a very complex operation with tomato plants in all different stages of growth and production. LOT of work!