Even I am facing the same problem. The overall message capacity is 500 SMS... :(

Samsung corby S3653 has 500 msg capacity and it has been divided between Inbox, Drafts, Outbox, Sentbox & My folders.
Inbox and My folders capacity - 200 text messages.
Drafts capacity - 50 text messages.
Sentbox capacity - 200 text messages.
Outbox capacity - 50 msgs.
Sim capacity - 20msgs
You can see this on ur mobile, just go to in ur messages & scroll down, in the last there is memory status. press memory status.
You'll see memory status. There is another option to scroll just besides the memory status. Press & select text message.
Now u can see ur text message memory status.

By Devendra Singh

Friend even i have the same problm with my corby phone. the only difference being that my phone gives such alerts at 230 messages. even i am annoyed by this problem. i m in search of the solution for the same.....do let me know if you get through ....and i'll do the same...

Samsung's SMS storege is tooooooo sucking btu i like the NOKIA's sms storage it can store up to 1000 sms not the parts in sms,

Maybe this will help you at least to check where is the problem. from your phone, press messages. select inbox, if you happened to see the messages appear with a little image just like your sim, it means that the messages are stored in your sim card. try moving messages from your sim to your phone, by pressing the inbox messages and once open, press more and you will be prompted with list of options, select move to phone and check..