The limit is 160 characters and there is no way to modify the limit and it will not wrap a long text into multiple text messages. If you really need to get around this you can send an email to the phone that will come in as a text. For example to a verizon customer you can send the email to firstname.lastname@example.org.
i have read of an app for blackberry phones called Beyond 160 which might help. This app is supposed to break a SMS message up into multiple messages if the message exceeds the 160 character limit.
While I haven't seen a free version of this, I have seen it available on Blackberry App World for about $7. It also has a 14 day trial period.
Please also be aware that I have seen reports that this app may not work properly with OS 5. i don't have any idea when Cannon software will have a new version out which addresses problems with OS 5.