It's not as simple as one thinks. Most (perhaps over 90%) of tomatoes "self pollinates" successfully. The stigma is enclosed within an anther cone. The stigma normally do not push through until the pollen has been shed, thus ensuring that pollen will land on the stigma below. However, some varieties have stigmas that do stick out of the anther cone - these likely require assissted pollination. Varieties of these include the potato leaved and the currant tomatoes. This self-pollinating mechanism may not be fail proof, especially if the tomatoes grow in overcrowded greenhouses with still air. This is because any vibratory movements involving the clusters of flowers do enhance pollination. Hence, if you grow tomatoes in the open air, subject to wind, and buzzing insects, it is not necessary to hand pollinate. However, indoors, you might improve pollination if you do. Various methods of manual "pollination" have been described. These include giving the tomato plant a good shake, shaking the clusters of flowers, to using any thing that vibrates. I suppose a "sonic" toothbrush (Sonicaire) would mimic a buzzing bee the best.
I am growing 9 tomato plants outside my apartment. My first crop was sparse. No bees around here I guess. I tried using a cuetip but that didn't work to well either. Then I just now tried my sonicare toothbrush and came back with a very yellow brush head so I assume that worked really good. All I did was turn the brush on and touch the back of the brush (not the bristles part) to the back of the cluster of flowers or a nearby branch. It was easy, I did all plants (40-50 flower clusters) in less than 10 min. So thanks for that suggestion
Pollinate the flowers everyday while it is warm and humid. Ideally, the humidity will be 65 to 70 percent. Greenhouse growers usually do this between 11:30am and 12:30pm (basically noon) when these conditions occur naturally. For them, early and late day pollination often will not produce proper crops. The tomato flower consist of two parts. The male anthers will drop the pollen. The female carpels will catch the pollen. The resource link below includes pictures of both and of tomato flower pollination. Most male anthers produce their pollen on the outsides of the anthers, making it easy to release pollen into the wind for pollination. In the tomato plant, however, pollen is produced internally, as if trapped in a straw. This is the biggest problem for tomato pollination. The plant needs vibration at the right frequency, such as the buzzing of a bees wings, to dislodge and release the pollen. Take an electric toothbrush to each support truss and main branch. The more pollen to successfully fertilize the plant, the more seeds will be produced in the fruit (and therefore the meatier the tomato will be). Larger tomato growing operations should consider bees for pollination.