126 volts sounds very close to a standard home voltage of 120 volts, which is single phase. 208v is a three phase voltage, and is the lowest I have seen. 240 is single phase (usually center tapped, so in your house you have +120, and -120 referenced to the neutral which provides the normal 240 for dryers, stoves, etc.).
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These voltages are both wye connection three phase voltages. The voltage difference comes from the primary three phase voltage supplies. 277 volts is obtained from 277 x 1.73 = 480 and 240 volts is obtained from 240 x 1.73 = 415. 480/277 volts is a common three phase American voltage. 415/240 volts is a European voltage. In Canada a common three phase voltage is 347/600. The 240 volts could also be a single phase voltage in North America derived from a split phase secondary on a distribution transformer that supplies 120/240 volts to homes.
The process of obtaining 220 volts from 380 volts is quite simple. 380 volts is a three phase four wire system voltage. The 220 volts is obtained by taking the sq. root of 3 which equals 1.73 and dividing it into the phase voltage. 380/1.73 = 220 volts. This holds true with any three phase four wire voltage system. 208/1.73 = 120 volts, 415/1.73 = 230 volts, 480/1.73 = 277 volts and 600/1.73 = 347 volts. This lower voltage is present on any of the three phase legs of the three phase system to the neutral which is grounded on a wye connection.
Let's get the terminology correct. A 'phase voltage' is measured across a phase, whereas a line voltage is measured between two lines. So there is no such thing as a 'phase to phase' voltage -it's a line to line voltage (hence the term 'line voltage').
The most typical three-phase voltage used in China is 380 V.
You Don't. 440volt 3-phase is actually 480 volts, taking a single phase gives 277Volts single phase. To get single phase 440 you would use one leg of three phase 440/760 three phase power.