ESD TVS voltage, current and power rating for portable device/mobile phone USB

[Wilson__]

What are appropiate voltage, current and power ratings for ESD TVS (transient overvoltage suppressor) for:

a) medium brand
b) top brand (like Samsung is top 3 mobile phone)

1. portable device interface pins like USB on mobile phone
 
2. human users can walk on carpet (to generate electricity) and air can be low hudmidity (in cold countries with home heater)

Application notes generally mention IEC 61000-4-2, level 1 to 4 and the new 4+ (better than 4)

Many thanks