According to their offerings list on their site, T-Mobile is now offering unlimited GPRS (packet data over GSM cellular) for only $19/month if you have a voice plan that runs at least $29/month.

They've also realigned their National Business plans:

Plan name	minutes	Cost/mo
National Business Plan 5000	5000	$129.99
National Business Plan 2500	2500	$99.99
National Business Plan 1500	1500	$79.99
National Business Plan 1000	1000	$59.99
National Business Plan 600	600	$39.99

All plans are $0.35/minute after the max (a big increase from the previous $0.20/minute, but a huge drop in the monthly and increase in the minutes at the high end), 500 text messages ($0.05/msg after that), 300 free weekend minutes (down from unlimited in some plans), and Unlimited T-Mobile to T-Mobile (except the 600 minute plan, which has 1000 minutes T-Mobile to T-Mobile).