Mobile nodes open by default "private" (unannounced) channels. That means are not "visible" in LN explorers. Node pubkey it is accessible (can send/receive) but also is private (not visible) in LN explorers. The "service" of course is not free, you will pay a small fee for opening that channel towards your private node. These inbound liquidity channels are used when YOU need more inbound than outbound. But you can also open FROM your private node a channel towards any other public node and little by little emptying that channel, slowly will became an "inbound channel" and used when is needed.