Keeping pay as you go alive outside of England

[Worm3rd]

TLDR: outside of England whats bare minimum I need to do with pay as you go to keep the phone number I was given and never lose it?

If you are reading:
First background: I’m American who will travel to England 2-3 times a year (I have a British girlfriend). I got an iPhone and a pay as you go service. I’d like to keep that number I was initially given, so that her friends and family don’t have to keep updating my number in their contacts everytime I visit 

1. I’ve seen/heard both that I need to do a chargeable action every three months and every six months.  Which is it?

2. What exactly is a chargeable action? Does topping off count? Do I need to send a text? Make a call? Use data? Keep in mind most likely when I need to do this chargeable action I’ll be in the States.  

[MI5 · Accepted solution]

@Worm3rd 

Top up and make a call at least once every 6 months.

[Bambino]

@Worm3rd You also might want to look at this: Discounted International Rates On Pay As You Go | O2

If you want to call the UK while you're in the US you're better off using WhatsApp, which is free over WiFi if the person you're calling also has the app.

[Worm3rd]

I use this phone only in uk. Unless when I need to keep it active.