T-mobile offers unlimited GRPS usage for $20/month, although I am very happy with ATTWS. You can use some phones to dial into an ISP, but the technology to do so is dated and is being phased out in favor of new packet-based technologies such as GPRS.

Many phones support getting your laptop online through GPRS, including mine. My hotel at E3 charged you per-minute for local calls, so I got online through GPRS. You can get my phone for about $150 through ATTWS.