Three (and possibly other networks?) appear to use aql in Leeds to convert to speech all sms that are sent to a landline number. This is annoying if your landline phone displays texts. And the calling number presented is 08443 585862.
aql explain in their FAQ, here:http://www.aql.com/site/faqs/sms-to-landlines/im-receiving-calls-regarding-sms-from-an-aql-0844-number.html

I've heard of the BT text to landline service, but didn't know that there was another one.

Texts can be delivered to landline phones in lieu of the synthasised speech call. I suppose that as the AQL service is (presumably) not connected and therefore "sees" all landline numbers as being ones it should play a synthesised message to. I know that Vodafone Business subscribers who have a landline number attached to their mobile get the BT synthesised speech message rather than having them delivered as a SMS text on the handset.