If you learn just the alphabet in ASL, you can say anything, even if you're slow! In the first round, I turn my hand around so you can see exactly what position my fingers are in; in the second round, I don't, so you can see how you would normally hold it to just sign to someone.
If you think it wouldn't be any faster to sign spelling everything out than to write back and forth to each other, consider this: when I was doing my medical assisting externship (read: that's an unpaid internship), we had a patient who had been a patient at that doctor's office for years come in, notepad and pens at the ready. I offered to interpret, and I only know a handful of words that I don't have to spell. The appointment took 45 minutes - and the patient and the doctor both said that was half as long as normal. Writing is slow. Signing is fast, even if you're not very good! :)
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