Oh, 3G data with a GoPhone SIM runs the same speed as an on-contract AT&T SIM. To get data, you need to
install a custom APN, then buy a data package for your GoPhone account.
I chose GoPhone over MVNOs since my cellular network usage is really low.
I get relatively few voice calls; I've been using Google Voice since before Grand Central was acquired by Google. The majority of calls actually ring my work landline. Outbound calls (US domestic) are free when I use the Talkatone app over WiFi.
At home and work, I have good WiFi reception, so really the only time I'm using the cellular data network is on weekends when I'm out of the house. My monthly 3G data usage appears to be about 100MB. I don't pay for GoPhone text packages since I get free texting through Google Voice. Plus, it's more cost effective to get GV texts via a data connection than pay for true SMS.
If I had heavier cellular network usage, I'd use an MVNO, but not Red Pocket which looks rather pricey. I'd opt for Straight Talk instead, which offers no-contract unlimited talk/text and at least 2GB of data for $45 a month. Straight Talk uses AT&T network (and Sprint for their CDMA handsets) and the chairman of the parent company (America Movil), Mexican billionnaire Carlos Slim has
personally encouraged iPhone users to switch to Straight Talk.
My current monthly cellular expenses are about $11-12 so it really doesn't make any sense for me to spend $33 more per month for unlimited service if I'm not using it. With GoPhone, I get what I pay for, and I don't pay for stuff I don't use.
Naturally, I had to pay full retail for an unlocked iPhone. However, my calculations show that my break even point is at 9.5 months.
Unlocked iPhone + GoPhone service
$849 handset + no activation fee + ($12/mo x 9.5 mo.) = $963
Subsidized iPhone + AT&T cheapest voice/data plan (no text) in November 2011
$399 handset + $39 activation fee + ($55/mo x 9.5 mo.) = $960.50
By month 10, I'm saving money. If I keep my iPhone for two years, the savings in total cost of ownership is $621 versus the cheapest on-contract plan. Plus, I am free to sell my phone at any time and it would command a higher resell price anyhow being factory unlocked.