Trial and error is a means to an end. And i have found that solution you require by accident.
Hmm…it seems that from what i can see from you guys you havent tried this before. It may only work in Australia, however its worth a shot in your country.
I use my mobile to log in and out of yahoo sometimes and i dont need to use gprs to do so. When i login i type “in [username] [password]” then send to special yahoo number as sms. This will log me in. Wehn i am logged in i get an sms telling me whos online but not who is invisible. By the way my phone is Nokia 6100. Everyone in my contact list is assigned a 3 digit number by yahoo mobile. If i select Options in my phone for the contact list message, then choose “Use Detail” which shows me the number of the sms, it also shows me who is online INCLUDING people who are invisible. It only takes me a few seconds to login and out with my mobile. I am still compiling my contact list, associating the 3 digit number with my contacts. Will keep you posted wehn i find an easier way. This method is still not fool proof.
Give it a try 😀