Why is it that every time I want to send a message on my mobile the wi fi disconnects.
Try the usual fixes for the home hub, in this order.
factory reset the home hub.
Then turn Smart Setup off.
http://bt.custhelp.com/app/answers/detail/a_id/443
Then separate and rename the SSIDs.
http://bt.custhelp.com/app/answers/detail/a_id/447
do you mean the wifi connection on your phone drops not the wifi connection from your router reconnects as soon as you send message could you have your phone set to use mobile data and not both mobile and wifi?