We are currently planning to implement direct routing with AudioCodes VM SBC. Currently we have no proper PBX system and therefore no proper IP Phones.
Are there any phones which already run Teams natively with Direct Routing? Polycom does have native teams phones, but they work only when the PSTN exit is the one provided by MS PSTN calling plans and not DR.
If not, are there "old" SfB IP Phones which work with Teams Direct Route? Such as AudioCodes 445HD?
technically SfB compliant phones are now working with Teams since early q3 (per MSFT SfB to Teams Roadmap).
I understand that YeaLink t56,T58,CP960, Polycom Trio 8500 & 8800 (speaker phones), & Crestron should all be offering Native Teams phones very soon. Polycom says their Native Teams desktop phones are due "Q1 2019". Many bluetooth headesets and earpieces are working with Teams Calling, not all have achieved full HID yet. Keep an eye on this page for updates https://products.office.com/en-us/microsoft-teams/across-devices/devices
Teams@nuwave.com if we can answer any additional questions for you, we are the first US Carrier endorsed by MSFT to offer Teams Direct Routing Hosted Architecture services so we have been working with it (and related issues such as your question) 24x7 for many, many months now.