Go into Asda or Tesco and go to the cigarette counter, ask for a top-up voucher and pay for it.
Chat with our AI personalities
All of them have phone numbers, but there are certain ways to get them. I would try looking up "how to get all gym leader's phone numbers in heartgold" on google
If you are a agent you can either use your spy phone to get to the HQ or go to the sport shop and click on the top curtain and when your penguin moves to it POOF your in the HQ but if your not a agent the catolog will come up and you will still be in the sport shop instead hope this helped
Go into build mode and click on the phone, then click on the area where the usual stuff (all the furniture) shows up. Then, go into the electric area and click on the same phone you had before and place it in the same place where the phone was before. May cost a little more based on how badly broken the phone is, but guaranteed to work.
Once you get to Mr Blacklock's house, view (through your inventory) the paper you tore from the phone book. It will have a 6 digit phone number for his company/house. Type this into the keypad.
You can invite roommates over (once you've finished the game) by picking up the phone and pressing the right button. I'm not sure what button it is, but I recall that it says it when you pick up the phone and have finished the game.