Not just Nokias
I've tried out 2 Orange SPV M700s, the models with a Magellan GPS device. They were ok in getting a 2D lock, but both are crap when calculating elevation, consistently reporting a figure about 60m too high.
Fine for SatNav, but no good with MemoryMap: When mountain climbing, it's worse than useless.
The T-Mobile equivilant, with a Sirf3 GPS, is much better