Sorry, I don't know of a free way to do this. But there's a work-around.
Swisscom has a plug-in for MS-Outlook called Desktop SMS.
http://www.swisscom-mobile.ch/scm/dlc-en…
It has an interesting option:
'Antwort als E-Mail erhalten' /'Receive reply as e-mail'.
If your brother agrees to share Swisscom's Desktop SMS application and an e-mail account with you, it could work for you too.
If you use Outlook as e-mail client:
1) Install Swisscom's Desktop SMS on your computer with your brother's cell phone number and e-mail settings! This will need a security installation code from Swisscom. Swisscom will send this code to your brothers cell phone.
2) Use Swisscom's Desktop SMS in Outlook to text a SMS, choose the 'Receive reply as e-mail' option, and send your message.
3) Your brother replies with a SMS, which the Swisscom gateway will automatically send to the given e-mail address.
4) You access the e-mail account with Outlook to receive your brother's reply.
Now, here comes the catch. As mentioned above, it's not free. Your brother will be debited for all your SMS. (0.20 CHF per message).