The only way to find your friend's mobile number is to ask him. Unless he has posted it on his Gmail or Google-plus profile, it is not publicly available.
Provided that the mobile phone has data access, you can simple go to gmail and access your emails. Depending on your phone model, you may also find a gmail app which makes emailing even easier.
You cannot remove your gmail account in android from PC. To remove it from android, you need Android only. In settings of android, you can delete it.
The status could be invisible for gmail. The status is what shows to others in chat. On desktop and mobile, the status could be different.
You can put a mobile number to make a Gmail. This makes the verification of the account very easy. It also helps you in the time of recovery.
You can put numbers on your phone through Gmail by keypad. You mobile number could also be added easily. The number of your mobile is not revealed to public.
You can delete a specific Gmail address from your android. Android places the google accounts in settings. There you can delete a specific record.
I think you will have to ask your friend to do that.
If you need to download Gmail for your mobile phone you will need to go to Google's Mobile website. They have the Gmail application available for download for a variety of mobile phones.
Gmail mobile is an application for a mobile phone or ipod touch where you can check your email from Gmail with either wifi or 3G internet services.
The clock near Gmail shows the current time. Android Phones have an application for Gmail too. The application manages the configuration of multiple accounts at a time.
Your mobile data could not be working. This might be the reason why Gmail is not opening. Gmail can only be opened if you have a working net connection.
Follow the instructions here: http://ashevillewebblog.com/tony/2009/07/gmail-mobile-on-the-motorola-i776-for-boost-mobile/