I know you guys are mostly talking about white label programs, but I really love the Trumpia affiliate program (affiliate, not white label). I'm perfectly happy making 25% commission rather than paying monthly fees for reseller rights. I was on iZigg, but after reading around here and talking to some people, I decided Trumpia was better.
I have looked around and the prices are sometimes higher than the competition (as far as retail packages, since I sell these as an affiliate), but there is also SO much more you can do. Most places offer only text credits, a few keywords, maybe two-way texting, and maybe e-mail, but it about stops there. You've got redeemable coupons, customer-specific appointment reminders, MMS, pre-recorded mass calling, e-cards, voting, surveys, text-to-screen (displays on big TVs, etc.), social integration, sign-up forms and widgets, QR codes, and much more. Not to mention an API.
I think all these extra features really help offset any slightly higher cost it may have. Plus there all 11 packages you can sell, from $25 to $1200 a month, from 500 credits to 30,000, and 1 keyword to 28. I know as a reseller you could make whatever packages you wanted, but again, I'm focusing on the affiliate option.
Plus there's a free trial option for your clients. I really like that selling point.