First option: Edit one of the contacts, copy the number, then delete the contact. Then open the other and paste the number into it.
Second option: Open one of the contacts, Edit it, scroll down and tap "Link Contact" and select the other to link to.
Thanks for your quick reply. I must be having a senior moment, as I can't see how to copy and paste the number, also Link contact does not seem to be available on iPhone 4 version 188.8.131.52
Thanks for your help.
The Link has been available since iOS 3 as far as my experience goes.
To copy anything in Edit mode hold your finger on it until a magnifying glass appears or double-tap on it. You can then select all or part of it.
If you are not in edit mode just hold your finger on the number and a "Copy" option will appear.
To paste (only in Edit mode) hold your finger on the field and "Paste" will appear.
These are basic operations, described in
To copy, tap the Edit button, place your finger a bit longer on the entry. A popup will appear and you can Select, Select All or Paste. After you made the selection another popup will appear and you can Cut, Copy or Paste. Choose Copy then go to the place you want to copy and do the same thing as before but now tap Paste.
Hope this help.
Many thanks for your help. As you have proberly gathered, I have not had my Iphone 4 very long,so I must download the instructions for iOS 6 as this has just recently been updated on my phone.
Many thanks for you help as I am still tring to find my way round my iPhone 4.