Is this correct english?

One of my friends texted me saying "Shall I call you?"

Shouldn't he have said. "SHOULD I call you?"

Because for whatever reason, "shall I call you" sounds like "will I call you" to me.

Also shall is used as an interrogative of let's.

"Shall we call em?" = Let's call em.

But "Shall I call you" makes no sense to me.