Some mobile networks can send a text to a landline, I had an odd thing happen with text several times.
I have my wife's mobile phone (not virign) it is set up with an sos button on the rear of the phone, that both calls numbers and sends sms texts message, when used it will both ring and then text all listed numbers. (ice phone with call assist)
Having put in my virign home landline number as well as my mobile number, when my wife presses the mobile sos button, rear of phone, (usually by accident or to test) it works perfectly and calls the virgin landline but the text comes through 3 day later as a computer voice message from a virgin telephone number. As we both have mobles it is not absolutely needed to contact the landline with a mobile sos button but not sure if this is advised, the sms message came through at 00.11am last night over 3 days late, a suprise!
SOLVED- A text can be sent from some mobiles to any uk landline phone.
My mobile phone MVNO virtual network uses EE and is not BT but any text message I send is converted to voice and sent from the BT text message to voice number, and may be specific to EE. (text to speech translation and relay system has existed for 20 years)
This means a text can be sent to a landline phone but normally it requires registration to the BT text messaging service.
I do not think virgin use this service or unsure which network they use,may be vodafone?
The BT number is similar to a virgin telephone number ending 1111 but different, hence the confusion, it is not sent directly by virgin media but via BT.
I have just tested this and it works instanly. The 3 day delay was probably because the phone was engaged so could not send the message and may not like answer phones. The BT text/voice number is also widely used for scams, so the call may not always be genuine.