I have had my htc Inspire for a couple of months and all of the sudden, I have a few (what appear to be random) contacts that can text me, but I can't text them (or even reply to their text). This is not on all of my contacts however, on the contacts that it's happening on, it happens all the time. As soon as I type in the text and hit "send", the "sending" icon flashes up for a split second and then my text stays in the draft. Any thoughts? It's making me crazy...

I you need to unlock the phone you should buy an unlock code for your HTC Inspire 4G from a trusted and safe HTC unlock service. The one i recommended have good prices.
After you have the code( just a few minutes), insert different network sim card. it will ask you for the unlock code. enter unlock code. Your HTC Inspire 4G will be unlocked and able to accept any GSM Sim card.
http://www.htcimeiunlock.com/htc-inspire-4g-unlock
http://support.htcimeiunlock.com/entries/20121711-Unlocking-and-using-the-AT-T-HTC-Inspire-4G-in-Europe

Happens to me and I take the battery out and re-insert it and boot it up and it works again. I havent lost any memory. This happens for no reason. Very aggravating.

A little more information is needed to properly diagnose.

Assuming that your service is current and the phone has not sustained any recent trauma (such as hard impacts or water damage,) check and make sure the phone is not in "airplane mode." This would disable any signal coming to or from your phone.
Second, turn the phone off, remove the battery, wait a couple of minutes, put it back together and reboot.
If that fails, I would back up all of your contacts, photos, ect... and download the latest firmware for your phone from the HTC website. This will do a complete wipe of your phone and return to factory settings.

Hi you can unlock your HTC inspire 4g by unlock code and for code you can contact Simpleunlocking and get codes to unlock your mobile..

under ur contacts put name with #...then it will show name

You won't get unlock codes for free, and people who claim to provide Free Unlock Codes for HTC usually give the wrong codes and after 3 or 5 wrong tries your phone will be permanently locked :)

I got my Desire unlocked from here, Fast and reliable service :)

http://www.myhtcunlock.com

Hi.
Reset your phone.

1. Power off the device.
2. Press and hold the Volume Down and the Power Button until you see the HTC logo, followed by white screen with text and a few menu options.
3. Press the Volume Down button to scroll down till you highlight "Factory Reset".
4. Press the Power button to restore your phone to factory settings and also your phone will restart.

Try using another SD card to see if that one will read. If so, there is a problem with your SD card.
But if that card is also unable to be read, and your phone is fully updated, there is a problem with the reader on your HTC handset. You can contact HTC for a repair or a replacement. You might even have some luck at the retailer where you originally bought your phone. It's a fairly new model.

Here's HTC's number:
866-449-8358 6am-1am Eastern Time

Hello J. Menger,

Please download the manual for HTC Inspire 4G Smartphone from the link provided below :

HTC Inspire 4G AT&T User Guide Download

http://member.america.htc.com/download/Web_materials/Manual/HTC_Inspire/Inspire_AT&T_WWE_UM_110218.pdf

HTC Inspire 4G AT&T Quick Start Guide Download

http://member.america.htc.com/download/Web_materials/QSG/HTC_Inspire/110217_Inspire_AT&T_WWE_QS.pdf