iPhone modify existing 'Phone' application

Change the existing "Phone" application that is supplied with the iPhone 3GS. Existing App has 5 icons across the bottom of the main screen. (Favorites, Recents, Contacts, Keypad & Voicemail) Modification required is to replace the "Voicemail" with "Messages". *** ADDITIONAL INFO *** Q1. Is it just a text change, or does the function need to be changed ? A1. The function needs to change also. When the operator taps that part of the screen, the app needs to needs to display recent SMS messages, instead of placing a call to the Voicemail phone number. The display of SMS need only be very simple, in plain chronological order. Q2. Should this be done in the Apple's native phone application that is shipped with the iOS ? A2. We could edit the native phone application, if that is possible, or we could replace the native application with a similar third party app. I don't mind either way. Only requirement is to have a quality phone app that integrates basic SMS and excludes Voicemail. Q3. What functionality does the integrated SMS need to provide ? A3. The SMS function required of the phone app is limited to only : + displaying the list of received SMS, + allowing the operator to tap a phone number contained in an SMS to call that number, + deleting an SMS. The existing "Messages" app will be used for all other SMS actions such as sending. Q4. What is the intention of the change ? A4. I don't use voicemail. Instead I subscribe to an answering service that takes my overflow calls, talks with the caller, and sends me an SMS. There are several source phone numbers used for these unrelated SMS, so the way "Messages" app groups them into 'conversations' is useless and detrimental. Other problem is that I touch the 'voicemail' icon accidentally as I am placing the phone down after use. Again this is useless and detrimental. I just want a nice, simple, scrolling list of my recent messages in the order they were received. I will browse through the recent messages, see who wants to talk with me, and tap on the number to call them back. Once the matter is resolved, I will delete the SMS.