Some weeks ago I more or less accidentally stumbled over a neat little tool called HeySms by Thibault Cohen. It’s written in pure Python, hence should be cross plattform, but actually it targets the Maemo 5 platform (i.e. the Nokia N900).

After all the tool bridges between SMS message transport and the Bonjour protocol. This is, if the N900 receives a SMS message it’s automatically passed on via Bonjour to a previously defined contact. Furthermore if this contact possibly answers via Bonjour, the reply is automatically forwarded as a SMS message.

The user interface is actually dead simple:

Screenshot of HeySms

It just allows you to select the Bonjour contact, to pass incoming SMS messages to, as well as a friend list. All friends are exported as Bonjour contacts, so they are visible in the contact list of the Bonjour client on your PC (I prefer Empathy). This enables to actively send SMS messages, i.e. not just keep answering.

After some initial problems HeySms really does a good job on my N900. I’ve sent quite a few pull requests to the author, which usually were integrated within hours. Really, really pleasing :-)

The most apparent problem was that incoming messages were not decoded correctly resulting in total gibberish being passed on to Empathy. Digging around a little I found out, that the software assumed a phone number length of 11 or 12 digits. Unfortunately my girlfriend’s number has 13 digits :-)

A second problem I quickly noticed was that the size of outgoing messages was limitted to only 70 chars. This is due to the SMS PDU providing space for a message payload of 140 bytes and HeySms using UCS-2 encoding (which means 2 bytes per character). I Initially solved this by adding support for concatenated SMS messages. Later I added support for sending GSM-7 encoded messages to allow for the typical 160 chars per SMS.

One last thing that really bugged me was that HeySms didn’t correctly work in the office. After quite a while I found out that the phone didn’t send multicast group joins as needed. It turned out, that the Linux kernel I had installed (which is the stock power kernel image, aka kp51) had multicast support disabled. After flashing a multicast-enabled kernel HeySms worked even there.

In case you’re interested, here are kp51 kernel images with multicast enabled:

If you’ve got a N900 and send plenty of SMS messages, give HeySms a try. You’ll definitely like it.