I bought a Powermonkey on a BA flight. Just loaded my Nokia E61 full of music and got battery low warning when boarding the plane It nicely charged the phone and I got to listen to my music on my long haul flight.

I have been carrying it ever since in my laptop bag (the charger adapter are useful for my traveling needs). The amount of adapters (monkey nuts) included nicely compensates for the price. (USB->Nokia is very nice).

Only bad thing is that the Nokia Big -> Nokia Small adapter is not exactly correct. The "spike" part is bit too long. It will change, but it does not attach to the phone as well as a original Nokia charger / adapter.

Toni

Ps. I have not actually tried this on my 770 just on a bunch of Nokia phones.