Conclusion: yes, for 'record shots'. For it to be slightly easier, I need to make a little adapter (which shouldn't be too hard).
Greenfinch on the sunflower seeds
Swallow wings and tails - sitting on the guttering above the window
Clouds on the horizon
With the vast variety of add-ons available, there must be some really good ones for birders. If you're in the States, you can get various fieldguides, but there doesn't seem to be much for the rest of us yet. Surely it's a matter of time?
Greenfinch photo taken with iPhone 3G S + Leica Apo Televid 77 with 20x eyepiece
All taken through double-glazing...