I remember reading a good article about this before but I cannot find it now. One reference I saw said if the pollen is dried first and frozen at -30°C it will keep for 12 months without much loss of potency.
This has been studied and proven that the lower the storage temperature, the longer the life of the pollen. There is also a similar linear relationship between pollen viability and storage humidity. Gelatin capsules can be purchased for the purpose of storing it. Tests have confirmed that it can be stored for as much as a year but more practically for as many as 6 months.
I have never frozen tomato pollen. However, I have frozen both Amaryllis and Daylilly pollen. I put it in small vial, cap it and place it in my freezer. I have no idea of the temperature. This I have found to be viable for one year. I have never tried to keep it longer. Using the same method, I can stare it for about 2 months in the refrigerator. Prior to storage, I just allow the pollen to air dry for 2-3 days.