...turns out that if you: ---enter a second phone number and/or:
---work your way through all six phone number entries, not necessarily entering a number, just entering
it seems to work fine. I entered the same cell number, 1 xxx xxx xxxx, a second time, this time without the two pauses. I worked my way through the rest of the numbers, hitting "OK" without entering anything.
I tripped the alarm and let the cell phone ring. It showed two missed calls. I reset the alarm, then tripped it again, and this time, I picked up. It was in the middle of the 2nd (of 3) reading of the message. I pressed a phone button a couple of times, and the siren quit. I walked toward the alarm unit and made some noise, and could hear it, so it worked.
Speculation: We live in a cellphone reception fringe area, and it often takes a bit for the call to go through. (Many people don't have the patience to wait for six or 8 rings. The X-10 may be this way.) It seems to take the system a while to locate your phone, so maybe you have to call it twice (or more) in succession before the provider's systems can locate your phone.
Conclusions: (1) Program your emergency numbers twice if there's a significant phone system delay where you live or are likely to be. (2) I wonder if a couple of pauses AFTER the number would help. ...think I'll try that next.