SIM only

[Chris__]

I have completed my contract and want to buy a SIM only contract but keep my phone number. 

Do I buy the SIM only deal first and then cancel my existing contract?

[Bambino]

@Chris__ See this guide: Migration & porting into O2 - O2 Community

Anything you're not sure of, call customer service.
Call 202 from your mobile or 0344 809 0202, 0800 902 0217 (Payment Management) or 0800 032 1402
When it comes to the reason you are calling, stay silent for 15 seconds and you will be taken to the keypad options.
Press 2 for Everything Else
Press 5 for More Options
Press 7 for Anything Else which will put you though to someone.
Say 'Upgrade', 'Lost/Stolen', or 'Fraud' if the suggestion above doesn't get you through.
Best time to call is 8 am.
You can also reach O2 via social media:
Facebook (https://o2uk.co/O2CFB), Twitter (now X) (https://o2uk.co/O2CTW), or Instagram (https://o2uk.co/O2CIG)

[jonsie]

@Chris__ 

Use USwitch

https://www.uswitch.com/mobiles/compare/sim_only_deals/o2/

Choose the deal you want

This will automatically redirect you to the O2 website

Just follow the prompts and choose the UPGRADE option

Complete the deal and nothing on your account changes except the tariff at the new cheaper cost

Payment date is the same and your next bill will be at the cheaper rate and will be made up of the pro rata cost of your old tariff and your new tariff

The change should show in My O2 within 24 hours

Volt benefits will still apply as will possibly a 3 month extra such as Disney+

[Bambino]

@Chris__ The advice from @jonsie is much better than my suggestion. Follow that.