I'm not aware of any limit - besides the character limit per SMS.
SMS is the abbreviation for short message service - with short meaning just that, and for that.
If you regularly exchange SMS that is over the 160 character limit (especially if well over the limit) with this person who has a Blackberry Pearl, you should consider using email instead. The Blackberry Pearl supports email exchange - at least in the interim until the cause of the problem is discovered.
If someone regularly sent me SMS that is well over the character limit and received as multiple SMS, I would ask - no demand that email be used instead.