Blackberry: A few of my friends send me texts which have a phone symbol instead of an sms text bubble symbol?

I have a blackberry bold and this happens with 3 of my friends who all used to have blackberries and were bbm contacts. they all got new phones so they no longer have bbm but whenever we text a black phone symbol shows up instead of the normal text bubble and my phone never vibrates when it receives their text. anyone know what this is and how to make my phone receive their texts as normal sms texts?