The Glebe telephone exchange is behind the post office, near the junction of Glebe Point Rd and St Johns Rd. It hosts Internode, iiNet, Primus, TPG, Telstra, and Optus DSLAMs, so there’s a good choice of ADSL2+ services.

For details, see adsl2exchanges.

I recommend Whirlpool’s Broadband Choice if you’re trying to choose an ISP.

A heatmap published by iiNet suggests no significant black spots in Glebe. But I managed to get a “non-portable” number from Telstra when I moved here, and had to have it changed before I could get Optus/Exetel ADSL.