Hi Tomy983,
So far I abandoned the MKR1500 in favour of a SIM808 Board (the AZ-Delivery one, it has 4G) + ESP8266 (NodeMCU Amica) and I use with an Ho Mobile SIM (Ho mobile - smart home plan). it works for my project but I'm not happy because it's not an optimized design (2 boards, at least 2A PowerSupply, at least a 2500mA battery when main power goes down...).
About the MKR1500, I didn't upgrade the firmware with the soldering procedure yet but maybe.... after that.... maybe.... I could be able to connect to Nb-IoT band with a 1NCE SIM card (that I bought from a reseller https://www.marcomweb.it/it/) but I cannot confirm that is okay because of firmware upgrade not yet done. In previous posts, some thoughs about 1NCE and the mess of finding someone selling NB-IoT SIM to consumers.
About firmware upgrade, soldering means altering the board and since I'm not confident about my soldering skills, I have contrasting feeling because this device should stay in my house 24h/7 for years and I don't feel comfortable, that's the main reason why I wait... but I know that an alternative solution could never come (at least in Europe because in US, one guy here in the forum developed a kit for upgrading the board without soldering: Modem Firmware Upgrade - Easy programming device project - #20 by adavidpglass)
Ciao,
Francesco