To get a guaranteed non-satellite circuit to the USA, useful for certain data transmission requirements which involve a lot of handshaking, dial 00 1 83 + area code + number.
The code 84 allows you to obtain a satellite link, if you really want one for any reason.
Simple answer. Yes.
Xmodem, YModem, and (old versions of) Kermit wait for acknowledgement after sending a block. When using satellite links the lag between end of block and acknowledgement appearing can be up to a second. With small block sizes (XModem uses 128 byte blocks; Kermit 96 byte blocks) this can impact on your throughput. New releases of Kermit permit sliding windows and the use of long (eg 2kB) packets these days. This is specifically designed for slow ack links.
Using a streaming protocol, like ZModem, gets around this problem. ZModem only sends acknowledgements back if there is an error, or at the end of a file.