I recently ported to VM after leaving Three where I also used WifiCalling with no issue. Ported to VM end of May, got the text advising WifiCalling set up and I do indeed get WifiCall on my display.
Heres the issue when on WifiCall - its an iPhone X (unlocked from Apple), I can send and receive messages via iMessage, no issues as uses data.
If I send a message to a non Apple device (send as SMS), it appears to go with no error. The recipient can get it straight away but sometimes delayed. If they respond, I don't get the reply until I'm back on 4G and only when they send me a further message and any outstanding messages from that sender, then they all come in.
Check the service centre number via another handset and is correct for the purple SIM.
Any ideas VM (or anyone)? I have done the usual reset network settings, reset phone, etc
Really interesting reading into your post, as It's something that have never been brought to my attention or I think anyone else too, so It's a good start haha. I've just ran a couple of tests, from my phone which is an iPhone X, to a colleagues phone which is an iPhone 8, 2 other people which have a Galaxy S10 & S9. Each on different broadband supplies also, we was able to send texts and receive them okay, there was a little delay but nothing which would make me think there was an issue.
Can you confirm with me if the person you are struggling to get messages from, is it just them or is it with anyone else?
I have the issue with anyone who is on SMS (non iMessage) and only when on WifiCall (works fine on data). They do not get a delivery receipt until delivered which can be late the next day. Once thing I have noticed and I advised the support team of is that the phone number format is incorrect. 07 345 35 67 89 as an example. If I turn on dial assist it thinks I'm in Belgium. The phone is correctly set up for the UK.
I believe its a SIM card issue. The SIM came as part of the Oomph bundle and the I ported my number to it a month later, so not a general run of the mill contract SIM.
Sorry to hear you're having problems with texting whilst on WiFi calling. I've had a look at your Mobile account and can see that you've spoken to an agent who has checked the settings and I can confirm that it's enabled also. I'm unsure whether you're still having problems but if so, can you try a different mobile handset to see if the issue is still there?