Have you tested the data services in more than one area or is it confined to that one location? You can complete the resets/updates without needing to call in. The first thing to try is to open your dial pad and enter ##873283# - send and let the phone complete a network refresh and test again.
If the problem persists, I would try doing a 'network reset' under settings>general>reset>reset network and let the phone complete hands free activation again.
If this doesn't resolve it, you can back your phone up (if not already backed up through iCloud) through iTunes and complete a phone reset.
If all of these fail, and data is still slow on the phone or text messages are delayed, you may want to visit an Apple retail store to have them test the phone or swap it out if it is in fact defective.
In this case, it sounds like it could actually be your phone. Dial *2 and see if they can reset your phone for you. I only say that because if you're brother's evo is faster (and it's not on 4g), then it suggests a phone issue.
Right now in my house we have a Windows Phone and an EVO and they are both super slow, we're both clocking in at 52 - 65 k on average which is just not acceptable. My brother brought his Verizon phone over and we clocked it at more than 800 k on average. So yeah, Sprint's pretty slow but SMS should be fine. Sounds like you could have a couple different things going on, but definitally call.
I've had the Sprint iPhone 4S for about 4 months now and the internet is VERY SLOW! I can't even check my FaceBook! It litterally takes 5 minutes just to log in. I use to be with tmobile and their internet was never this slow! I cannot believed people talked me in to switching to Sprint. Can anybody help please? Is it my iPhone or is it just Sprint? And if it is just Sprint, what can I do about it? Also, I have been noticing I am not recieving text-messages very fast and my brothers Evo recieves texts like 100x quicker!