Originally Posted by Motorcycle Mama
What that poster is likely seeing under SMS option is the SMS History (Number of Previous Items) which is the number of messages in the current "conversation" (ie from a particular recipient/sender) that will show up when viewing an SMS message.
yes. he's checking options --> SMS, and changing "number of previous items" to 50. that means it'll show up to 50 SMS messages between you and that person that sent the message. kind of works like an IM conversation.
to answer the original question, you wont have to worry about the # of SMS messages on your phone. I have 4,465 SMS messages, and that only takes up 1450.4 kb of data (40 mb free).