Samsung Galaxy 5 - Having Major Issues with Text Messages (Sending & Receiving)

I have had my phone for quite a while and it just recently stopped sending/receiving text messages. It actually seems to coincide with the timeframe that the new software was rolled out. Every time I try to send a text message, it gets stuck in the send and just spins. I have no idea whether the text is sending or not. At times, it appears that the text actually sends at some point because sometimes I receive a response back before my message says it has sent. Other times, I don't receive messages until hours later than when it says it was received. I have tried the following and nothing has worked:

(1) Restarting

(2) Clearing the cache on the Messages app

(3) Turn off Wireless

(4) Turn Airplane mode on and then off

I recently found a post about changing the APN data on the phone. Can't tell if this is working yet or not. Prior to this, my phone was set to ATT Nextgenphone (MMSC=http://mms.mobile.att.net and MMSProxy=proxy.mobile.att.net). What is the correct one?

Name: ATT
APN: wap.cingular
Proxy:
Port: 
Username: wap@cingulargprs.com
Password: cingular1
Server: 
MMSC: http://mmsc.cingular.com
MMS proxy: wireless.cingular.com
MMS port: 80
MCC: 310
MNC: 410
Authentication type: 
APN type: default,supl,mms
APN Protocol: Leave it to the Default one