Haven't had any issues using hot desking (forced login) and a 5610/5621 IP phone. In fact my primary phone is a VPN enabled 5610SW and I am a hot desk user.
Kyle Holladay
ACA-I, ACA Call Center, ACS-I, ACS-M, TIA-CTP, MCP/MCTS Exchange 2007
ACE Implement: IP Office
"If it worked the way it should you wouldn't need me