Word Choice – Call On or Call At or Something Else?

Both are semantically correct as they are. But compare

I'll send it to you.

and

I'll send it you.

The second sentence wouldn't make sense in formal writing, but is found to be understandable in northern England spoken usage. There is also the case of

I'll send you this thing

Which flow much better without the to. In this light it might be more prudent to use send to you, as it is more formal, but send you in your context would also be accepted.

EDIT: I precised my conclusion and added one example following precisions made in the comments.

• Please call me on this number. You can reach me on this number.

Acceptable everywhere, principally used in UK/Australia/New Zealand. Sounds strange to North American ears, but understood.

• Please call me at this number. You can reach me at 0088000900.

Acceptable everywhere, principally used in US/Canada. Might sound strange to English speakers outside North America, but widely understood.

• Please call me through this number. You can reach us through this number.

Usually used when the caller will need to speak to an intermediary before being connected to the desired party (such as when a receptionist answers all incoming calls). Not generally used when the number connects directly to the desired party (which is "DID" Direct Inward Dial in North America, and "DDI" Direct Dial-In elsewhere).