That device is GPRS (2G) only. Telecom is WCDMA (3G) only. These devices are very outdated - they won't work on Telecom at all, and might work on Vodafone but they are using technology so old you shouldn't even consider it.
Thank you both, I really appreciate your guidance As you see I am quite clueless when it comes to cellular, and VOIP in general not much better.
We have an old Portech GSM gateway in service now, working happily to link our Trixbox system with the Vodafone network. I'm considering a change to XT (who seem to have dramatically cheaper plans for smartphone use), but it'll require an upgrade of this box.
Is there a good, modestly priced 3G alternative you'd recommend?