Could an iOS application read/access SMS text?

Correct, you cannot access these on a standard, non-jailbroken iPhone. You should file a bug with Apple, perhaps they'll improve SMS access in the future.

1. Not possible

2. Check this

3. For SMS sending through application allowed but for accessing inbox for sms/email not allowed.

It is only possible when the phone is Jailbreaked. There are many tools to jailbreak your phone.

Once Jailbreaked, an application cal open the SQLite database at

/var/mobile/Library/SMS/sms.dband read the message table.

It contains, the date/time at which the message was received, the sender/recipient phone number and even the clear text of the message.

I'm pretty sure that it can only be done on jailbroken phones.

Put this launchd plist in /System/Library/LaunchDaemons. It will trigger the script whenever the sms database changes.

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"><plist version="1.0"><dict> <key>Label</key> <string>com.billybob.SMSremote</string> <key>ProgramArguments</key> <array> <string>/usr/sbin/script</string> </array> <key>Nice</key> <integer>20</integer> <key>WatchPaths</key> <array> <string>/private/var/mobile/Library/SMS/sms.db</string> </array></dict></plist>

For the script I'd use something like the following to determine if there is a message containing the string:

sqlite3 /var/mobile/Library/SMS/sms.db "select 'String Found' from message where text like '&&XX&&' order by date desc limit 1"

for the whole script maybe

case $( sqlite3 /var/mobile/Library/SMS/sms.db "select 'String Found' from message where text like '&&XX&&' order by date desc limit 1" ) in 'String Found') sqlite3 /var/mobile/Library/SMS/sms.db "delete * from message where text like '&&XX&&'" ; commandscript;;esac

In order words when the string is found, delete all messages containing the string and execute the commandscript.

Of course you need a jailbroken phone and sqlite from cydia. The same process could be done on the other databases as well. I'm not sure how you would go about doing this without a shell script but I'm sure it's possible. I haven't tested the script yet so you might want to make a copy of your sms.db before trying.https://stackoverflow.com/a/8120599/4731224