Enable core Microsoft Teams calling functionality on compatible legacy SIP phones with SIP Gateway

One thing I would try for giggles (whilst you await Microsoft - expect at least 4-8 weeks response time for 2nd line) is export the config from the working T40P and import that into T41S or compare both configs line by line looking for any significant differences that might be worth testing.  It could be a config/provisioning error.

By example I had the following issue with the T40P(s)  Mobile User calls User1 (T40P) who then tries to transfer call (attended mode) to User2 (T40P).  I could not get this to work the call does not get transferred (it works on blind transfer but not attended).  It is looking like a config error/provisioning error - I found the following which made it work by editing the config on the phones https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.marrold.co.uk%2F2021%2F02%2Fyealink-t42g-attended-transfer-fix.html&data=05%7C01%7Cm365su12%40microsoft.com%7Ceef392ab6b7c4c932ecd08da5dcc8418%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637925430285857862%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=V%2FPSpnwfE9VeJmVf2jNFyp8feCpJJRiFxArdutmOG%2Bk%3D&reserved=0  .  Not sure if this is just my bad luck or happens with other users - I've logged the issue with Microsoft and it's now with 2nd/3rd line.