This is a known problem with ICS (up to 4.0.3, I think) :
If you follow this link you'll also see a solution to the problem (I'd recommend backing up your contacts first, just in case):
- Assuming your phone is synced with Google Contacts
- Disable contacts syncing. From the home screen: Press Menu -> System Settings -> Accounts & sync
- Erase all contacts from the phone: From the home screen: Press Menu -> Manage Apps. Scroll down to Contacts Storage and press Clear Data.
- Restart the contacts sync as in Step 2.
I also have a Nexus S and am in the UK and have just had version 4.0.4 rolled out to me yesterday, I haven't had a chance to download it yet BUT 4.0.4 should have 'Improved phone number recognition' according to the Android team, I'm assuming that's a reference to the problem we've been having and should fix it. Here's the link to statement from the team:
Here's another solution, that's been posted on the top link I gave you, I haven't tested it personally but others in the thread seem to have and have said it works. Try the first shorter one before this though. Here it is:
1- menu --> people
2- option --> import/export
3- export to storage --> OK
4- option --> import/export
5- import from storage --> after searching
6- import one vCard file --> ok
7- choose the file which you exported early (00001.vcf) --> wait for import
8- now your issue is solved and you can try if it works with you. but we got another error of duplicated names here.
if you want to solve the duplication on names here. follow the below:
1- menu --> settings
2- accounts & sync
3- enable the sync and choose to sync your gmail account
4- after finishing the sync. go to your laptop and open your gmail email.
5- press on the contacts tab on the left side
6- select all the contacts --> more --> find & merge duplicates