Putting aside the tethering...the phone with the SIM...can it browse the internet?
If not then start there with APN settings.
If so then maybe add ,dun to the APN Type in the APN settings.
Find your phone on this list:
Officially Recognized APN Reference
If your phone isn't there maybe these might work:
APN Settings:
Name: Mobile Internet
APN: sp.mb.com
Proxy: Not set
Port: Not set
Username: Not set
Password: Not set
Server: Not set
MMSC: http://aliasredirect.net/proxy/mb/mmsc
MMS proxy: 74.49.0.18
MMS port: 80
MCC: 302
MNC: 220
Authentication type: Not set
APN type: default,mms,agps,supl,fota,hipri,dun
APN protocol: IPv4
APN roaming protocol: IPv4
APN enable/disable: APN enabled
Bearer: Unspecified
MVNO type: GID
MVNO value: 4D4F
