Until the thirties airspeed was generally measured by a strut-mounted vane. This device was, as you can imagine, less than accurate and prone to huge position errors, but in a biplane with a stalling speed of 45kt and a VNE of 90kt this wasn't too much of a problem - anywhere in the middle would suffice for most purposes. Your 300 ton airliner is a different beast, sadly.
In a large airliner, especially at lower altitudes, is a stall basically curtains?
Actually no b. It is, as c rightly points out, an instrument that indicates the difference in air pressure of the two environments it monitors. That airspeed may be inferred from the data is undeniable, but that doesn't make it a flowmeter. A flowmeter measures actual flow. All in the name d'ye see?
An airliner behaves like any other aircraft really, so it's simply a question of whether one has sufficient height to trade for airpseed. In short, the lower the height the less the chance of recovery. (Let us not go into possible complications of a deep stall scenario in a swept wing aircraft.)