700 something for upload is not that bad... you can skype video almost perfectly w/ another person w/ just 375 just not HD. I think the problem comes with the iPhone using the same connection IP as another computer that may have been asleep then awaken or in use in your wifi network... You could try an static IP connection on the iPhone to see if it improves and also close any other electronic that might be using your internet access since they will make your upload problems worse... Are you facetiming w/ the persons on the same wifi network? what happens when you use another wifi? if it was an upload problem then the quality should be bad, not just disconnect the whole facetime conversation after the min, or is it that after 1min the quality is crap?
And yeah your internet is slow...