Hello,
UCI functionality is described here.
When run via CLI, the command UCI commit is used to apply the changes. However, in SMS utilities, it seems like these changes are applied automatically after the initial SMS command is sent. So to rephrase the initial suggestion, the UCI command via SMS in your case should look like so:
<admin_pass> uci set network.mob1s1a1.apn=ibox.tim.it
The router should then reply via SMS:
Updated option: network.mob1s1a1.apn=ibox.tim.it
If it does not, there may be something wrong with the configuration. Are you able to access the router remotely?
Best regards,
DaumantasG