You may be experiencing any of these issues:

• Dropped calls or no mobile internet access
• While connected to LTE services, outbound calls take a long time to connect
• SMS and/or MMS services are slow or not functioning
• Low signal bars

Ensure the phone is fully updated by following these steps:

1. Go to Settings and select System Updates. The exact path will differ depending on your phone.
   These are the three typical paths:
   
   Settings > System updates > HTC software update
   Settings > Software update
   Settings > AT&T Software Update
   
   

2. Select HTC Software Update to check for new updates.
   If an update is available, follow the on-screen prompts to download and install the update.
   If no update is found, confirm that the device is on the latest software version, by navigating to Settings > About > Software Information.

Updating the Preferred Roaming List (PRL) will refresh the list of towers the phone prefers, and may also resolve issues with signal.

NOTE: The process for updating the PRL may differ between GSM or CDMA phones. Check with your network provider if you are unsure whether your phone is GSM or CDMA.

Follow these steps to update the PRL for GSM phones:

1. Press and hold the POWER button until the Phone Options appear.
2. Select Power Off and wait for the phone to fully turn off.
3. Wait for a few moments, and then turn on the phone by pressing and holding the POWER button.

To update the PRL on CDMA phones, find the option in Settings. Follow these steps to update the PRL for CDMA phones:

1. Navigate to Settings and select System Updates.
2. Select Update PRL to begin updating the PRL.
3. The phone may reboot after this procedure.

You may experience temporary network disconnections and slowdowns the following situations (this is normal network behavior and does not indicate any problem with your phone):

• Making outbound calls. When connecting an outbound call, the phone must first disconnect from the LTE network. This may take up to an additional 5 seconds compared to a phone not connected to LTE.
• Switching from 4GHSPA+ to 4GLTE. 4GLTE uses a different algorithm to determine how many bars your phone displays. When moving from a 4GHSPA+ to a 4GLTE network connection, you may see a change in how many bars are displayed.

Environmental factors are also a likely the cause of the network connection issues if the issues only occurs in certain conditions or places. The following environmental factors can affect network performance:

• Distance from the tower can also affect signal strength.
• Signal strength weakens over distance, so being closer to the nearest tower will improve signal strength.
  Howeer, if you are directly under a tower, you may not receive the signal from the tower due to the nature of how the signal is broadcasted.
  

Contact your network provider if you continue to experience a poor network connection.