What is a Vanity Address?
Just a gimmick, but a nice one: your own custom XRP Ledger account address starting with your name / handle / brand. Instead of a random account address (starting with a lower case r) you will have an account address that starts with a lower case r and then a short value you like.
How are Vanity Addresses generated?
We generate millions of addresses per second specific hardware (GPU's) with custom software.
When I purchase a Vanity Address, do I get the secret (private) key?
No, you don't. You don't need to: the XRP Ledger offers a feature called "rekeying", "setting a Regular Key". This means an XRP Ledger account can authorize another account (key pair) to sign on its behalf.
Isn't it a problem you have the generated private key?
The XRP Ledger also offers "disabling the master key", deauthorizing the private key natively belonging to an account. We do both, ensuring only you can sign with your Vanity address. This renders the native private key we generated (and have) useless.
How do I import a Vanity Address into XUMM / how to import on a new phone?
See this FAQ article:
TL;DR: Import it as a Read Only account using the r-address, and make sure to import the Regular Key you configured during your purchase as Full Access account.
What if I have more questions?
Contact XUMM Support, using the XUMM Support xApp inside XUMM, or submit a support ticket.