Checking data usage (UK) on a dumb phone - SMS option?

[carlosp_uk]

UK Three Mobile customer here. I got my 12yr old son a dumb phone for phone calls, emails and texts only. Set him up with a SIM only plan with me as the account holder. Now he wants to know how to check his data balance — obviously he can’t use the Three App, and has no access to websites. So how does he check his data balance? Is there an SMS option to do this? I can’t seem to find one in the online help documents. 

[q4quality]

Pay as you go balance checking was available through SMS by sending BALANCE  to 333, but Three appears NOT to be supporting it anymore (as in July 2025). The SMS to 333 still goes fine, but no response comes back. 

USSD balance checking option was never available in Three, due to legacy reason - if am not mistaken.

So as of now, calling +44 7782 333444 from the phone with simcard inserted and pressing option 1 is the only way to know the payg balance without registering for online account servicing. (SMS to the number wouldn't work either)

[Geluk]

Only by looking online [via pad\ laptop], on your account section of their website; search bills.
Assuming it's not PAYG of course, where you don't get bills.

[carlosp_uk]

That requires a web browser - my son has a dumb phone, so it’s phone or SMS only