I don't eat the frozen dinners (Lean Cuisine, WW, etc) for that very reason. One dinner can boost you over the 2300 limit very easily unless you make sure the rest of the day is not salty.
You know I've been keeping track of my diet on Sparkpeople and I can track sodium. Most days now I keep it under 2000. I'm always amazed at the sodium in places you wouldn't expect.
8 oz low sodium V8 = 140 mg
1 C Honey Nut Cheerios = 269 mg
1 C soy milk = 170 mg
2 slices of light wheat bread = 230 mg
1 slice cheddar flavor veggie slice = 220 mg
When you have to deal with numbers like that even on healthy foods those frozen meals don't cut it.
That's why you have to fill in the blanks for a diet with lots of fruits and veggies since they are very low in sodium as a rule.