>The probable mobile code may work in Europe - here it's 064, 060, 0677, 064 and such, I've seen 09x in Croatia, and ISTR there were such prefixes in Belgium. In the US, however, the mobile providers have local area codes, so your landline and your mobile have the same area code.

Well, mine do, but my kids still have the mobile numbers from the phones we got them as teens, and haven't lived in this area for decades. I remember when #2 went off to college and the first mobile phone bill came in and I couldn't figure out why he was calling people all over the country, until I realized that like him, they'd all arrived with mobile phones with their home area codes. (Also, of course, my kids have no landlines. Oldest did in his first post-college apartment, but none since.)

> Really hard to guess which is which, looking at the number. There's probably some lookup table somewhere, from which you can find that out, but we never bothered, as it's probably changing from year to year and it may also cost some to get, and would require maintenance for... not much of a gain at all.

The original rule for US area codes was that the middle digit was 0 or 1, which allowed their phone company systems to detect fairly quickly that you were dialing with an area code. That's no longer true, though still the case that no area codes start with 0 or 1. The list is widely available, though it does change as the number of phone numbers continues to increase and area codes have to be added. (This site seems to have the current list, for example: https://www.allareacodes.com/area_code_listings_by_state.htm.)

Tamar