Yes, it supports simultaneous connection to 2 devices. After the Boom Go 3i is connected to one device, a short press of the speaker's Bluetooth button will connect it to a second device.

When dual connection is enabled, audio will pause when switching between devices. You can enable/disable this feature in the app by going to More Settings > Dual Connection.

Note: Dual-device connection is unavailable in TWS or Auracast broadcasting.