Hi -
Just to put my two cents in: there is a standard for this, E.164, that HubSpot should adhere to.
Put simply, this an international ITU-T recommendation for the worldwide public switched telephone network. In other words, it’s what the telephone companies use. No more than 15 digits, excluding the international call prefix. Prefix with + to indicate that the country calling code is included.
The neat thing about this approach is that DNS mapping is then possible, i.e., any phone number can be mapped into a domain name, after which DNS queries can can locate the Internet service facilities to accept and process phone calls to the owner of record of the number, allowing direct end-to-end internet connections without passing to the public switched telephone network (and any fees they might charge. Unfortunately, not all countries support this, but some major European countries do…
John