u have to use QPST software,

and tweak this:

E398 original:
NF_PREF_MODE_I
0
14

NV_BAND_PREF_I
0
896

u need to tweak both to value below:
NV_BAND_PREF_I ( Both value) 
0
0

NF_PREF_MODE_I ( Both value )
0
14

then your E398 will be on UMTS2100 only 

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Added on December 28, 2012, 3:36 am MTU for TL-MR3420 V1 & V2 

QPST software can tweak all Qualcomm chipset modem/phone,... as long as the QPST software able to recognize it,..

what other model modem  u are refering ? 

USe Aircard Watcher

u can try with QPST sofware,

if the QPST sofware can read  your 320U, then it will work,