I’ve done it! I’ve forgotten my iPhone 4 as well. So naturally you’ll want to check your voicemail if you’re without the phone for a few hours. Luckily you can check your voice mail from another phone.
1. Dial the phone number for your iPhone.
2. Wait for the voice mail greeting to start, then press * (star).
3. You will be prompted for your password. Enter it.
4. Follow the instructions and use the phone menu as needed to listen to your messages.