Hi Andrew,
Since Tealium is a client-side technology, we can't tell which country the user is coming from (this information is not available within JavaScript). However, some content management systems (e.g. Drupal) have the ability to output the user's country code into the data layer, and you could then base your content modification rule upon that information. If you have specific domains for each country, you could also use the domain to determine which number to serve (.e.g if domain ends ".co.uk", serve the UK number), but this method obviously doesn't guarantee that the user is in the country of the site they are visiting (unless you have automatic country redirection).
There are also a number of tags in the tag marketplace that can provide this service for you. ResponseTap is one such vendor, and they also provide analytics services, so you can tie up your website visitors with people who ring in to the contact centre. Other products are available - I'm just giving an example of one that I have worked with and I know works.
Hope this helps,
Craig.
Check out our new Swift integration library for iOS, macOS, tvOS and watchOS: https://github.com/Tealium/tealium-swift with updated
documentation https://community.tealiumiq.com/t5/Swift/tkb-p/swift.