It's not fully reliable. For example you can have local residential lines that in practice go over VoIP and the provider allows you to use the same account to call out. They'll be classified as just normal landlines. It will vary wildly from place to place, but I think soon the type field in HLR will mostly lose its meaning.
(Just checked my company number, running on a hosted PBX, and it's marked as landline with no extra porting info that would contradict it)