There was a mention of this here, http://www.dmr-uk.net/index.php/announcements/
it is not a feature I have tried yet so am keen to know feedback on if it works as described.
Updated post from DMR UK 12th June 2017
There seems to be some confusion how text and call alerts work on Phoenix UK. The platform now uses a routing table which keeps track of where users last transmitted from. Unlike before, you no longer have to text or send call alerts on the same Timeslot as the other user is on. You can now send them on either timeslot and the messages will send to the user via the last repeater the person you are sending to was using. If you are mobile and wish for people to keep in contact with you, please when changing repeaters make a short transmission to TG9990. This will ensure users all get the text messages and call alerts they are sent.