Ken

I've done quite a bit with UPS Worldship.

Actually, they integrate with you by mapping to your customer and order tables and fields.

They print shipping labels using your data and will send back charges and tracking numbers to the tables and fields you specify.

Call your client's UPS Rep and they'll send someone to do it at no charge

UPS' competitors do likewise.

If that doesn't work for you and you want to go the other way, there are some 3rd party apps that do that too, but the price of the vendor-supplied option - FREE - is fairly persuasive.