I always have my mail program running, so email me and ask is the most reliable approach. But off course, there's a delay at each end, it can cause unsightly mail pileup, and all in all I'm keen to find a more efficient approach.
I've given up on MSN Messenger and ICQ equivalent, but I've been experimenting with PING, and with using the DynDNS dynamic DNS service.
Use the following command from a DOS or UNIX/LINUX prompt -
PING bendr.homeip.net
Usually, if I'm NOT online, this domain name will resolve to an IP address of 128.0.0.0, resulting in an invalid destination message from PING.
If I am online, and have remembered to do my DNS update, the domain name will resolve to my current valide IP address, and PING will report successful contact with my PC.
If I've gone offline but not remembered to do the DNS update to 128.0.0.0, then a valid destination IP will be found, but either no contact will be made, or possibly contact will be made but with some other user coincidentally allocated the same temporary IP address as I last had. I apologise for any confusion this ends up causing.
This is a new experiment, but hopefully, clicking this link while I am online will take you to a web-page hosted on my home pc.