Transferring Contacts Using Google Sync:

Using a Google account, you can sync the contacts stored on the HTC Desire 600 with the account, allowing you to then re-sync the contacts with the HTC One M8. This is one of the easiest methods of contact transfer and it can be applied without needing a computer

1. Sign in with your Google account on the HTC Desire 600
2. While on the home screen, swipe the "Status" bar down using two fingers
3. Tap "Settings"
4. Swipe to "Personal" and then tap "Accounts & sync"
5. Tap "Google" and then select an account
6. Clear and mark the "Contacts" check box. As an alternative, you can tap "Menu" > "Sync all"
7. On the HTC One M8, register the same Google account
8. From the M8's home screen, tap "Apps" and go to "Settings"
9. Tap "Accounts & sync" and select a Google account
10. Allow the account to sync contacts with your One M8

Using the "Import / Export" Feature:

You can use HTC's "People" application on the Desire 600 in order to export the contacts stored on the device, in the form of a vCard file. The file can then be sent to the HTC One M8 via email or through a computer, and can be imported via the same "People" app on the One M8

1. Launch the "People" app on the HTC Desire 600
2. Go to the "People" tab and tap "Menu"
3. Tap "Manage contacts"
4. Tap "Import / Export contacts" > "Export to phone storage"
5. Select an account, and make sure you remember / write down the file's name before tapping "OK"
6. Open the email client and compose a new email
7. Attach the vCard file to the email and send it to your own Gmail address
8. Switch to the HTC One M8 and open the email containing the attachment
9. Download the file and then launch the "People" app
10. From the "People" tab, tap "menu" > "Import / Export contacts" > "Import from storage"
11. Browse for the vCard file and import its contents to the One M8's phonebook

NOTE: after you have created the VCF file on the HTC Desire 600, you can transfer it to the HTC One M8 by connecting both smartphones to the computer via USB, and manually copy-pasting the file from the Desire 600's memory, to the HTC One M8's "sdcard" directory. Then, launch the "People" app and import the file

Using "Send Anywhere" to Transfer Contacts:

"Send Anywhere" is a third party application that can be used to transfer various types of files, including contacts, from one phone to another via a P2P connection. This method doesn't require access to a computer.

1. Go to the Google Play Store and install "Send Anywhere" on both of your smartphones
2. Once the application has been installed, open it on both smartphones
3. On the HTC Desire 600, tap "Send" > "Contacts"
4. Choose the contacts that you wish to share
5. Tap "Send" and choose the method of transfer. You can tap "Receive" on the HTC One M8 and input the randomly generated transfer code from the Desire 600. As an alternative, you can tap "Generate QR Code" on the Desire 600, and scan the code with the One M8's camera to commence the transfer