I used to be able to recieve texts above 160 also, but now i get the same message. I'm with Verizon. I think something was done on the last firmware upgrade from motorola.
I did a search on Text message limit and came up with an old thread that spoke about how everybody else (Verizon, Tmobile, etc.) splits up the message into 2 seperate texts, but AT&T sends and recieves the full message all at once. No one on that thread seemed to be experiencing what we're experincing now. That's why I think its something new.