I do not think that will work. For the same reason sticking an iPhone SIM with active Data in an iPad will not give you data on the iPad.!
Can one use an iPad AT&T sim in MIFI device?
Sim size not accounted for would the MiFi need to be unlocked and GSM
or if an AT&T MiFi just stick it in?
Sierra Wireless AT&T Elevate Unlocked LTE 4G MiFi GSM Mobile Hotspot