There are a couple of things you have to look at:
#1: your domain name.
Every single domain name is case insensitive. Always has been, always will be. You cannot capitalize a domain name in any way, shape or form (whether a .com or a .tel)
#2: Display on the telproxy.
The telproxy tries to capitalize the display of your subdomain links (subdomain links within the page ONLY) in the following way:
every dash is replaced with a space, and first letter of every word is then capitalized. So xyz-abc becomes "Xyz Abc".
Note that for #2, there is absolutely no way we will ever try to guess the capitalization of a (sub)domain. Imagine for example johnnysmith.tel
It could be:
Johnny Smith
or:
John Nysmith
We can't guess it, and we won't guess it.
That said, note that soon we will allow labels for .tel links (i.e. subdomain links). Then we'll be able in the telproxy to use those labels as the main display for the links, which will allow you to capitalize to your hearts' content.
Thanks,
H