Here are the best 02 APN and MMS settings for HTC One and One Maxx, these should also work for Galaxy S4 variants and Galaxy S4 Mini. htc one best ringtones  

Try this

1. Tap the Applications key 2. Tap Settings 3. Tap Mobile network 4. Tap Access Point Names 5. Tap the 3 dots on the Top Right of the screen 6. Tap Reset to Default 7. Tap Access Point Name again 8. Select O2 Pay Monthly or O2 Pay and Go 9. Tap Access Point Name again 10. Tap the radio button beside the correct APN

If that one above doesn’t work, then you can try entering it manually (look at example below.)

1. Tap the Applications key 2. Tap Settings 3. Tap Mobile network 4. Tap Access Point Names 5. Tap the 3 dots on the Top Right of the sceen 6. Tap New APN 7. Tap Name then tap the text box and enter O2 Pay Monthly then tap OK 8. Tap APN then tap the text box and enter wap.o2.co.uk then tap OK 9. Tap Proxy then tap the text box and enter 193.113.200.195 then tap OK 10. Tap Port then tap the text box and enter 8080 then tap OK 11. Tap Username then tap the text box and enter o2wap then tap OK 12. Tap Password then tap the text box and enter password then tap OK 13. Skip past Server as this is preset as Not set 14. Tap MMSC then tap the text box and enter http://mmsc.mms.o2.co.uk:8002 then tap OK 15. Tap MMS proxy then tap the text box and enter 193.113.200.195 then tap OK 16. Tap MMS port then tap the text box and enter 8080 then tap OK 17. Tap MCC then tap the text box and enter 234 then tap OK 18. Tap MNC then tap the text box and enter 10 then tap OK 19. Tap Authentication type and tap PAP 20. Tap APN type and type Internet + MMS 21. Press the 3 Dots on the Top Right of the screen 22. Tap Save 23. Tap the circle next to the new profile so that a green dot appears in it 24. Press the Back key four times to return to the main menu.